Hmmm, really tough to say what could be going on with this precious baby. So wonderful that you have her.
It's a big adjustment and dogs do get depressed, so partly it could be that. But, given the sort of neglect she came from and questionable eating and health care - who knows what may be wrong.
I don't think I'd give her turkey slices though bc they're probably very salty and contain a lot of preservatives or other things that may make her sick. To stimulate her appetite, you could even give mashed potatoes or white rice. You could home cook some meat or fish, but I don't really recommend prepared meats. Otherwise, if you could get some quality canned foods like Wellness, Natures Variety or something, that would be good.
Do you mean her tummy feels "hard"?
I think given her history, I'd probably get a basic chem panel if it were me.