Please check this link out
I would think she could have coccidia this can come out in a pup when it changes homes.
I would try to get your vet to treat her ASAP with albon and see if this helps.
I would have her stool checked but even if it didn't show as positive I would treat her also check for giardia. Your girl is failing to thrive you can loose her if you don't get her to start thriving. I don't intend this to scare you but you need a vet who understands toy breeds cannot go on like this she needs help.
It is not normal for a pup to not eat, that is a sign of a problem,
Try a different vet
http://www.beaglesunlimited.com/beag...occidiosis.htm
Deana
Prestigeous Yorkies