Just try to get her drinking well. I'm glad that she is eating better. Many vets aren't that familiar with chickens. My daughter is a vet, and she admitted that all she remembered about chickens was bumblefoot and how to crop feed them. Some vets have their own chickens and may be more knowledgeable, but in the past seeing chickens was not very profitable, since you can buy another for $2-3. Avian vets may have more knowledge, but some vets are getting into the backyard chicken thing nowadays, due to the popularity of chickens. There are a few vets here on BYC, and most have chickens.
Are you giving her any vitamins and some probiotics since she was treated for cocci? Those help to get the gut back into shape. Was she vaccinated for Mareks disease? Here are some links to read about Mareks which can cause loss of balance, paralysis of wings or legs among other symptoms: