Good god! She looks awful. I would do a fecal check on her to make sure there isn't some sort of parasitic thing going on. If there isn't she will gain weight quickly. I also take on rescues and our last case was bad bad bad and they are almost fat now. Even The worst can be brought back with the right care. I wish you guys the best of luck! Go slow and steady and shell be better in no time.
Check out what's new on my website... www.Homegrownscales.com