Mother dog pretty much starving herself since losing her puppy 4 weeks ago...is there anything that will help?

I've never had a bitch give their pups more than a thought once they've weaned them LOL. They're usually only too happy to part friends.

Is the bitch spayed...and if so when was that done? Have they checked her temperature of late? does she drink water? What has been tried to stimulate her appetite exactly? Perhaps she is simply waiting to be offered something better...

Do the people she is with...walk her often? Does she have mental stimulation and physical exercise in their home? Do they have other pets/dogs and if so how does this bitch react to them?

I've never heard of a physically healthy dog starving itself to death for any reason.  Vet check, ASAP.

Edited to say that I re read your post and it's been 4 weeks since the pup was adopted.  The mother dog would be dead if she hadn't eaten anything in 4 weeks.  Tell your friend to quit feeling sorry for this dog.  That's not helping the dog and may very well be hindering her emotionally.  Get her out and about.  Enroll in a class and start working on the things the dog needs to be adopted rather than focusing on what happened with the puppy.  Dogs don't carry around the same kind of emotional baggage humans do and feeling sorry for her won't help this dog.  Dogs do suffer from depression at the loss of a companion but it doesn't usually last long and can be mitigated by the humans by keeping her mentally occupied and physically active as Gina suggested.

All I can tell you is what i witnessed and was told while I was over there.   They do have one other foster at the time.  A 5 year old Great Dane.  But she has never paid much mind to the Dane nor the Dane to her.  

 She was spayed pretty much a few days after she was brought to the foster home.   And she has been fine up until the day the puppy left.    She has been to the vet several times in the last few weeks since the puppy left.   She checks out perfectly healthy other than the significant weight loss and no appetite.    At this point she barely will drink anything.        She just lays there and stares out the window all day.    They do take her for walks and she was always a good walker as long as they had her now she just walks behind of goes a little bit and lays down, goes a little bit and lays down.

 She was a very friendly dog when she came into the shelter, now she doesn't want much to do with anyone.     They have tried a few different foods to get her to eat and she just won't touch them.    They are at the point of force feeding to atleast get a little in her.   But she doesn't want it.   And they tried the whole put the food down thing and then take it up 20 minutes later, when she gets hungry she will eat.  It hasn't worked.

She was doing so good with her obedience training (the foster has her in Obedience class) but ever since the puppy left, she just lays there and won't even participate in class.

Obviously there has to have been something to cause her to be so close to that puppy.    But they said the day that puppy left she whined and whined and kept trying to get out for hours.  And after that nothing, its like all life left her.  She just lays there, by the window.  Its like she is either just waiting for her puppy to come back or she is waiting to die.

She was at the vet again Tuesday and they ran all sorts of tests and everything so far points to her being healthy other than the not eating. They are still waiting on a few tests to come back.    The decline was rapid in her.  Very rapid.    The vet said he has only seen this in one other dog, and the dog eventually just died.   The dog was one of two dogs raised together from the same litter.   When the dogs were 4 years old, the sister got hit by a car and died and the other sister just quit.   Within a few weeks both dogs had died.     He said it may just be one of those things.

She completely started refusing all food about a week ago before that she would eat a little at a time.  Again they had been force feeding her and coaxing her.  But now she completely refuses and as of the last few days she may take a few drinks of water but barely any

All i am saying is she is not well and appears to have lost all interest in life.

They treat this dog the same way they have treated all their fosters, they encourage them to join in, they give her daily walks, lots of love.  And again she is going through obedience classes but now is at a point where she won't even participate.

 Its not like they are just letting this happen or they are coddling this dog.  

Again I am pretty far removed from the situation.  I don't know the specifics all I told you is what I was told or understood of the situation.  I saw the dog today and I have never seen anything like this before in my life and I have been around a lot of dogs

In complete honesty this sounds SO much like pyometra it's not funny -- They may have done "tests" but I wonder if they have re-tested for pyo (it can be hard to catch at first) ... OR that when she was spayed something was simply done 'wrong'. 

This doesn't really sound behavioral -- it LOOKS like it, but dogs generally just aren't wired that way.  The birth of puppys sounds like this huge emotional thing to US -- but it is a BIGGER **physical** thing to a dog.  All kinds of things can "happen" during birth -- wounding, and infection can be huge.  And that then comes on gradually -- and with pyo in particular it tends to simply come on as a "withdrawal" by the dog.  I have again and again, heard stories just like this -- always described as the dog pining after puppies or a former owner/caretaker -- but it IS infection.  It just comes on slowly and incidiously and the dog is then more and more withdrawn.  It IS painful --

Agree that thorough medical evaluation is key.  If infection is ruled out... They could try using Nutri-Cal, which is a high calorie paste supplement.  Smelly food, such as tripe (Tripett), will tempt some dogs to eat.  Any chance of her visiting the pup occasionally, just so she can see that it's still alive? Any chance the adopter would take the mother dog, too?

Some people swear by "satin balls":

http://www.holisticdog.org/Nutrition/Satinballs/satinballs.html

What kind of dog is it?  How thin is thin?  (I ask b/c some people might look at my dogs like I starve them while a conformation judge might say they are "heavy";)  Where is the dog kept?  Where is she when she is pacing?  What kind of exercise, training, and mental stimulation is she getting?

I think in order to move forward, the foster people need to look beyond the loss of the puppy.  With dogs there is very little point in trying to figure out why a dog acts like it does.  Sometimes there is no logical reason.  It doesn't really matter if the dog grieved the puppy or not, that will not change what course of action needs to happen in order to help her move forward.

Not knowing the answers to my questions, if this were my dog I would impose a strict routine (which helps the dog because it becomes predictable), I would do plenty of exercise so that the dog is tired rather than pacing.  My GSDs will pace for hours if they are bored and haven't been tired out, and they have nothing like the loss of a friend to blame it on, that's just their temperament.  Offer the dog food a few times a day for 10 minutes or so.  Leave the food with the dog and leave the dog alone.  My Kenya won't eat if she feels stressed or pressured.  In new places I just crate her in an empty room and put the food in her crate.  I would not force human interaction.  Ignore the dog and give it treats when it initiates interaction but do not shower it with praise or coddle it.  If it was a street dog it might take a looooong time to understand human interaction.

Abbeyroad86

But they said the day that puppy left she whined and whined and kept trying to get out for hours. 

(1)  Did she do anything else to ease her anxiety - like get into things or chew on things?  Are they missing anything like socks or a piece of a blanket that smelled like the pup?

The reason I ask is that this sounds like an intestinal blockage.  If so, eating may cause a lot of pain.  Has she been xrayed?

One member's dog actually ate fish-smelling sand at the beach.  The sand finally passed a little at a time (without the puzzled owner or the vet realizing that sand was the blockage on the xay) and the dog recovered.   A second, milder episode (when the dog was caught eating sand and developed the same intestinal problem) resulted in an end of the dog's trips to the beach. 

(2)  Have they considered a experimental treatment - an antibiotic, painkiller, or antidepressant - just to see if it makes a difference?

If the foster does lose the dog, they might consider letting the vet do a surgical exploratory.  The vet might do it for free just to to try to find an explanation for the dog's behavior.

Sure hope they find the problem in time to same the dog!!!