Remember a long time ago....

Reporting to the ACO is more likely to backfire.  If you watch those animal cops shows, they make it clear that even in dire situations, they cannot remove a dog from someone's property without clearance from law enforcement in one form or another, or owner relinquishing rights.  (Risk that the dog/evidence might be concealed/removed/destroyed before the proper law procedure is followed must be clear otherwise.)  If they report to the ACO, he/she will likely say the same thing and require the dog to be returned unless/until the current owner(s) relinquish their rights to the dog.
 
Sounds terribly convoluted, but that's the way I understand it is in most US states.

Thank you all for your replies. Delilah is doing great... she is eating (although not as much as I'd like... maybe it'll just take time, I'm sure she's still adjusting to having regular meals?) I've added a little more canned food to her diet to entice her to eat. I think she's scared someone (maybe Dusty?) is going to take her food.. the whole time she's eating, she's looking around and hunkering down.
I've learned that her favorite toy is tennis balls. She loves them. She plays with them, destroys them and plays with them some more. She's a character.
She and Dusty are getting along great. He's still looking out for her, this evening. He's following her around and has even playfully barked and "growled" at her.
BIL or his room-mates still have not called concerning her. Hubby's mom talked to BIL this morning and he made no mention that she was gone, only that he had to get the rest of his stuff out of his house... so I know he's been there today, and surely by now, they've realized she's gone.
I'm not going to involve animal control or the police if I can help it. It's sad, but the reality of the matter is the room-mates take excellent care of their own dogs... but just didn't have the attachment or concern for Delilah, apparently. I guess they found the extra dog, especially one that is not theirs, to be more of a burden? What a shame.
Oh well...
BTW.. we've had only one complaint so far, concerning sweet miss Delilah... she's a ball buster.. litterally. She's already popped two of my duaghter's balls, lol. It upset Poptart (my daughter) at first, but then when the second one was torn to shreds, she just shrugged and said "She's just like Murphy, ain't she?" For those of you who don't remember, Murphy was another GSD we had (also a dog BIL tired of and wanted to get rid of). He had to be put down last October, due to nerve injuries associated with tail jerk syndrome after being hit by a car.

I think she's scared someone (maybe Dusty?) is going to take her food.. the whole time she's eating, she's looking around and hunkering down.

 
mehpen - you might already know this information, but it's worth repeating. []  When we got Roscoe he seemed scared someone was going to take his food -- he'd been a stray in the woods for a while and at his previous home the other dogs tended to bully him.  We used this method to get him calm about food.  It's from "Lauri S" of rawdogranch.com
 
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Here's the approach I use with my fosters when they get food protective. I want them to learn that me approaching them while they have food is a GOOD thing. And this method has worked the best for me so far.

I give them a recreational bone and let them get started on it. I have a container filled with small chunks of raw meat. As the dog is actively chewing on their bone I walk BY them - not straight at them and no stopping - just walk past them. As I walk past I say "Hi Puppy - is that a good bone?" in a happy voice and drop a piece of the raw meat right at their feet. Keep going (don't stop) and then let them be for a minute or two.

#1 most important thing - NOBODY, human nor canine, likes to be 'bothered' while they are eating. Pester me enough while I'm enjoying my steak and *I'LL* snap at you!

Ok, so back to the dog. You keep up the walk past and drop raw meat for a few more passes. By now the dog should be actively looking up as you approach. After all - you walk by and manna falls from your hands!

Once the dog is actively looking up at you, you can stop in front of them, talk to them for a second and then drop the meat and move on.

How quickly you move from step to step will all depend on the dog. You want to avoid ANY confrontation at this point. If the dog growls at any point - you went too fast to the next step. Go back and work more on the previous step.

So - here's the steps.

Step 1 - walk past, no stopping, drop meat and keep going
Step 2 - walk up (again, not straight AT the dog), stop, drop meat and then move on
Step 3 - walk up, stop, bend down, drop meat, keep going (in this step you get closer to the object being guarded)
Step 4 - walk up, bend down, place meat NEXT TO the bone while talking in happy voice, get up and move on
Step 5 - walk up (at this point you can walk straight at the dog), bend down, take hold of the bone with one hand while you offer the dog the meat with the other hand, release the bone, get up and move on
Step 6 - same as above only this time you will pick up the bone and then give it back to the dog AFTER you give them the meat
Step 7 - same - but now you pick up the bone, give the meat, hold the bone for a moment and then give it back and move on
Step 8 - Pick up the bone, take a step away, step back and give the bone back and give the meat

Notice how by the end you are giving the meat AFTER you get the bone - that's important. You have transitioned the dog from getting treated for nothing (in the dogs mind) to getting treated for NOT guarding the bone.

Now, once you get to this point you can incorporate the NILIF program - asking the dog to do something in order to get the bone back.

To me, this is the most non-confrontational method of TEACHING a dog that they do not NEED to guard their resources.

*jensw... thanks for that info, I'll give it a try.
*Delilah is still doing well. After a trip to the vet it was discovered that she has hookworms, an infected scratch near a back tooth, on the gum line in her mouth, minor hip dysplasia and a minor skin allergy, most likely a result of malnutritio, and has a boarderline thyroid issue that is most likely a result of her age, that we will just be keeping an eye on.. She is on antibiotics and I've been given a wormer to give her first thing in the morning (it may upset her tummy, so I will wait to give it to her when she can spend plenty of time outside.) and the vet also recommended a senior vitamin, once a day. The vet thinks that once she starts recieving regular meals and builds up her condition to a more suitable level, the skin allergy may resolve itself. He says he's seen lots of malnourished dogs develope allergies as a result of the malnutrition. Right now he gave me some shampoo to bather her in until it clears up.And guess what? No heartworms. (the room-mates tried to say she has heartworms and that's why she's in such bad shape.) She only weighs 41 pounds, our goal is to get her up to 62-65 pounds.
*She ate really well this evening. A whole can of food mixed with about a quart scoop of dry food... which is really impressive for her, she's been just picking and acting really shy around her food. I think she's on the verge of trusting us all.. even Dusty.
She and Dusty played hard together this evening... and Dusty is helping us teach Delilah some tricks, such as speak. LOL, they're a hoot... and both work for tennis balls!
Delilah is a ball hog though, several times I caught her running around with TWO tennis balls in her mouth and Dusty following behind waiting on her to drop one, lol. I'm thrilled that they are getting along so well.
*Hubby did talk to BIL today. At first nothing was said about her, but then Josh told BIL that I was taking her to the vet today. He says BIL acted really concerned and said he was glad we took her and would give her  a good home. He did offer to pay for the vet bill and anything she needs.... but we will be declining that offer... too little, too late if you ask me. And then he said he and his new friend were looking for a home where they could have a large pet... yeah, right, like he'll be getting her back. And hubby told him not to expect for us to give her up. He says he thinks BIL understood and he kept saying how lucky she was that we took her, and how disappointed he was in his ex room-mates. He accepts no responsibility for her condition, Hubby says. BIL is completely blaming his ex room-mates.  Funny how he seems sooo concerned now, but just three days ago he couldn't have cared less. And how can he NOT be held responsible? After all, she was still HIS dog.. the room-mates were just doing him a favor by keeping her, since he moved into a place that didn't allow for large dogs.
Well, whatever, I'm sure they'll all get what they deserve in the end.
*Oh, and by the way, Delilah got a fancy new, collar today. Black leather with "diamonds" and a "diamond" encrusted charm. She looks good in her new "bling". Very fancy, and very classey.

By golly, I'd MAKE him pay for the vet.  MAKE him take some danged responsibility for this animal he so easily abandoned.

I feel like if we accept his offer to pay, then when he finds a place that will allow him to have large pets, then he will try to take her back with the understanding that we were just dog stitting, or keeping her while he couldn't. This way, we can say "Hey, you left her, you didn't take care of her or make sure she was being taken care of. We feel there's more to owning a dog than just forking out money after the damage was done.... we appreciate your offer to pay her vet bills, etc.. but we are her owners now and that responsiblity rests on us." I know if we accept his offer he will try to take her back, later down the road.

Just wanted to let you all know that Delilah is doing good. She's already becoming protective of us and our home. She was standing at the fence barking at a delivery man this morning. I called her to me and she came right away, but was very wary of the stranger. I guess that's a characteristic of the breed... most all of the GSD's I've owned have been this way, although as I remember, it took them a little longer to develope that bond with us. But anyway, I just wanted to let you all know that she is doing well.

I am happy to hear she is doing so well.  It sounds like she is happier with you by the second and it was great you were able to get her!

Tomorrow will be the first time we've seen BIL since we took Delilah. We have dinner with their mother every Sunday. He asked us to bring her with us... she will be staying home however. I just don't feel right about him seeing her or being around her right now. I'm still a bit pissed with him. What do ya'll think? Am I doing the right thing?

I would just not waste my time thinking about you BIL and how negligent he is,,,,just enjoy your new dog...because you and your DH are her angels!!!

I'm just seeing this and I think it's great of you to take Delilah and to be so loving and protective of her. You're right, he should take responsibility.. that fault does not lie solely on the roomates.. he should have been checking on her regularly if he truly cared and he would have seen the situation and done something about it himself. Even if his idea of a solution if he saw it was to ask you to take her he would have at least made the decision in her best interests instead of showing "concern" afterwards.
 
But, the most important thing is she is in a loving home, has a great new friend in Dusty and in your family. Give her some hugs from me and bless you for taking her in.

Just wanted to let you all know that I finally broke down and let Delilah join us during our evening walk... she did great. Actually better than Dusty, lol. The only problem we had was with her trying to "pull" towards other dogs that were barking at us. Other than that, she did good. We walked for about 20 minutes, she wasn't acting tired when we got back, ate some dinner and took her usual spot in front of my chair for a short nap before the guinea pig caught her attention. She didn't eat all of her dinner, but I left it down for her maybe finish later. I just feel so bad leaving her home while we walk with Dusty  so I decided to slowly introduce her to our daily routine. We did cut our walk short, by about half. She did good. But if any of you have any suggestion on how to keep her attention on me and off the neighborhood dogs, I'd love to hear it.
We had dinner at my mom-in-laws today.. BIL and his friend were there. He did ask how she was doing but didn't really show too much interst. He didn't even ask where she was or if he could come see her. Oh well, his loss is our gain!
I ran into a mutual friend this morning and was telling her about us having Delilah now and everything that had happened. She told me she would let "Steve" know.  I had no idea who this Steve was, so I of course asked. It turns out that a lot of what BIL had told us abut Delilah was a lie... from where she was born to how he originally "adopted" her.... I guess he didn't realize I was friends with this woman who know so much of Delilah's history. I'm still debating over weather or not to tell him I know the trusth or just let his lies go? Really what he told us was really nothing we believed (not all of it anyway) but still, it made him seem more important and his dog more special. Not that she isn't a special dog but you all know what I mean.

I would NOT let him see Delilah again.  It's very selfish of him and does nothing but make himself feel better.  Very unfair to the dog to let her see her prev owner and think maybe he's back.  For good or for bad.
I WOULD get him to put something in writing that he's relinquished her to you.  But I'm a CYA kind of person and would rather have it in writing than worry about a battle in the future.  Just make something up like the town won't let you register her without proof of ownership transfer.

That's a good idea... I think we may do that. Since dogs do have to be registered with the county here, I will tell him that there has been lots of people reporting stolen dogs (true) around here lately so before I can register her with the county, as a new pet addition, I have to have a statement from him saying he has given her to us. That's a good idea. Thanks.. and very nice dobe you have there!

Aww, it's so kind of you to take her in.  .. what a sad situation, it's a good thing DH happened by.  I don't have any great advice that hasn't already been mentioned, just wanted to cheer you on. 
 
It warms my heart to hear that this girl has gotten a good home.