If I remember right it's been less than two weeks since you've had her. I know with chinchillas they can be slightly off their diet for two weeks just because they are moved to a different home. I have a feeling it is pain and stress causing the problem more than anything at this point. I recommend trying another week of syringe feeding and carefully tapering off medication used to stimulate her bowels. The side effects of baytril can take a week to wear off as well.
At this point I think Oxbow pellets is the best diet considering most pet store diets are terrible and you really have to go out of your way to find the best food for chins. If she was on something different I doubt it was good. You can try different varieties of loose hay including alfalfa, bermudia, fescoe, and timothy. Loose hay should be the main portion of a chinchilla's diet although many chins will eat mostly pellets. I recommend alfalfa for a while and then switching to timothy or something less rich once her weight is up.
