Growled at me for the first time

Well, let me just say that Ruby is adorable BUT, I do understand.  The first growl I ever heard from my lab was also chewing a raw bone.  Guess they're pretty yummy to them huh?  My lab's about 80 lbs and there was no way I was going to push the issue right then.  I went to the frig a few min's later and got something out that I knew she'd like and worked on trading for the bone.  I've done that every time since then and she's much better now (no more growling since the first time).  I also worked on making her feel comfortable just with me being near her while she chewed on the bone.  It took a little while before she'd quit moving away if I got close and eventually I could sit down and she'd come eat it at my feet.  For me, it's about gaining their trust.  I know others who feel that it's our right to say what you get or don't get, but with a full grown lab, I'm not going to risk her arguing about that and me getting bit [].
 
I think your reaction was normal, so don't beat yourself up.  However, what may happen if you continue is that Ruby will figure everytime you come near her when she's chewing a bone, bad things happen (bone goes away, I go in crate).  You don't want that to happen and you don't want her to feel that the crate's a punishment.  So, my suggestion is to work on trading her for high value items until she feels that your presence isn't a threat to her enjoying her treat. 

I think your reaction was normal, so don't beat yourself up.  However, what may happen if you continue is that Ruby will figure everytime you come near her when she's chewing a bone, bad things happen (bone goes away, I go in crate).  You don't want that to happen and you don't want her to feel that the crate's a punishment.  So, my suggestion is to work on trading her for high value items until she feels that your presence isn't a threat to her enjoying her treat. 

 
I totally agree with Cathy.  Aussies (at least the original working Aussies) are dogs with strong herding and guarding instincts, and some will get testy about special stuff.  Dogs that will let you take kibble out of their mouths may draw the line at a marrow bone.  It's not unusual, and it's not abnormal, but you need to train her to accept the presence of humans around her stuff.
The best protocol for doing this that I have found is the one in Jean Donaldson's book "Mine! A Guide to Resource Guarding in Dogs".
Best to get going on this training now, as this behavior can escalate and make a dog quite dangerous.  With dogs that are known to be guardy, the safest place for them at times when guests are present and there is food about is in their crates.  Don't take the chance that a three year old will drop a french fry and try to pick it up at the instant the dog decides its on the floor so must belong to her.

I feel your pain - each of the few times Wesley has growled at one of us, I am shocked and then very upset (growling at others - now that is a different story []).  I think the hardest thing is to walk the line between wanting your dog to know you are the boss, it is your bone that you are letting them have and that they need to have no problem having you near it or giving it back at any time...  and the issue that no dog is going to want some person around them that they associate with taking all the good stuff for "no reason."  I think its probably best, with most dogs, to try to make the dog totally comfortable with you around its stuff first (a resource guarding protocol like - next few times you walk by drop an even better treat, then go give her the even better treat when she has no problem with you walking by, then trade the even better treat for the rmb, then take the rmb and then give the even better treat and then give the rmb back - waiting until she is comfortable with each before moving on to the next).  We are working on this here too and I have to say, although I have not gathered the courage to try with a rmb, we are currently working with squeeky balls which he used to run off and guard if we threw it and he is now playing great fetch, almost never running off to guard the ball, he is bringing it back and dropping it - because he gets even better stuff when he does - and usually he gets the ball thrown again too...
 
I would think that for a normal dog, just being made to feel really comfortable with people all around, even touching and taking, their stuff, because they associate it with getting even better stuff is probably the way to go...

Do you ever try to touch her or play wth her food while shes eating?  I do this to Bailey about every other day... I will giver her the food and wait a bit hen pet her, then walk away and come back and talk to her and say gimmie dat Baiwey and take some of her food from her bowl... she usually just keeps eating or will move to another area of the bowl or will stop for a sec and look at me.  I will grab her head and kiss her head while shes eating too....
 
I dont do this constantly while shes eating or anything because I certainly dont want her to think Im annoying (and I know she just wants to enjoy the food) but I do usually do one of those once in a while just to make sure nothing is changing and that she is used to it... same with bones.  With bones she will move away or not she doesnt really seem to care what I do.
 
Maybe if you dont usually touch her while shes chewing a bone this would be something she just isint used to... I would start going by her while she eats bones and if she growls I would say HEY! NO! and the just keep petting her.  I think some people might not like this idea but it worked with my moms dog and she eventually quit.

Gosh, and mine have to be told that no they can't lay on the sofa with me to eat their bones......

LOL I dont make mine get down I just clean up the mess []

I would play around with them too when ever they have something like a bone in their mouth or something they chew on. I would let them get really chewing on it then start petting and touch her near her butt then work up to the head. I would also take it away to after she has been chewing on it so she gets use to it and wont snap at anyone.
 
If she snaps at you or growls I would shake her head by grabbing the back of the neck skin  or the throat area to correct her.
 
I did this with Blue after he snapped at my brother with one of his chews now you can take almost anything from him and he doesn't mind.

I have to tell Chase "no thanks" when he drops his half-chewed, bloody bone on my lap.  Uck.  []
 
I think that the trading thing would be a good idea!  I did that with Chase when he was still a puppy as preemptive resource guarding training.  Now I can say "what's that you've got?" and he'll drop his bone at my feet and look up at me, rooing and talking, in hopes that I'll give him a treat.

I think I rather have a half chewed bloody bone then cat poop dropped in your hand!![&:]

I won't scruff a dog for any reason and I'd sure not scruff a dog with a valuable resource.  But mine are taught from the time they are tiny that I control the resources and that if I want something its mine for the taking.  This truely is never an issue for us.  Like I said, if I didn't tell Tyler and Sheba that the couch is not the appropriate place to eat the raw chicken, they'd be in my lap with theirs!

Thanks for all the great responses! I haven't had a chance to respond yet as I had to work last night but I realize that I should have said in my OP that from the day Ruby came home we started working with her to prevent these types of issues from coming up.  I read quite a bit about it before we got her and my MIL's dog is the perfect inspiration for what NOT to do and I am determined that Ruby will be different. Starting from day one, she was often hand fed her food, even by my boys.  We are always talking to her and interacting with her while she's eating whether it be her bones or her kibble.  We very often will ut our hands in her bowl to add something yummy like a liver treat so she equates hands in bowl with good stuff.  Her bones have never been an issue, either.  I often have to move them while she's chewing on them because she scoots all over the kitchen floor towards the dining room and I don't want the bone on my wood floors.  Similar to what Glenda said, she tries to chew her bone on my lap - she's my velcro dog.  She has never, ever shown any type of guarding or agression before this incident. I'm fairly certain that I just startled her yesterday.  She had her back to me and was pretty intently chewing on the bone for about twenty minutes or so and I realize now that I hadn't really been interacting with her, just glancing up every few minutes or so to make sure she was alright.  I think she forgot I was even there and when I patted her, it scared her.  When I mixed her veggies into her dinner last night I did it while she was actually eating it and she didn't seem to care one bit, just kept on eating.  Same thing with her egg this morning.  And we often play the trading game which our obedience trainer taught in class. This is something that I definitely don't want to escalate so we'll keep doing what we've been doing and I'll make sure not to sneak up on her again.  I've already talked to the boys about this as well.  I think I will get the book Anne recommended; it looks interesting and I'm sure it'll be helpful.  I'm sorry I was so dramatic in my OP - I didn't have a lot of time but should've at least given you all some background on what we had been doing with her.  Given all that we have been doing, I was really shocked. Thank you all so much for your responses, they're very helpful.  It's great that I can count on people with so much experience.  If you have any other suggestions, I'd love to hear them. Christi