Feed some Poultry Cell vitamins. Could be a vitamin B deficiency. Could also do human Vitamin B Complex instead of the Poultry Cell vitamins. Half a human pill per day until condition improves, pop it in her mouth.
I've not encountered this situation myself, but there's a lot of info on this forum, and that's the standard recommendation. If it's not an injury or bumblefoot, most likely culprits are vitamin B deficiency or Mareks. Since you don't have paralysis, Marek's isn't as likely at the moment. If she improves after the vitamin treatment, you'll know that was it.
For future prevention, if she improves with vitamins, I question whether your feed has sufficient B vitamin nutrition. Could be old feed, where the nutrition has degraded, could be the vitamin content wasn't sufficient to begin with. If you post on here how you're feeding your chickens, folks can help out with that. Also it's a great topic to search on.
ETA: I just realized I was assuming your birds don't have worms or coccidiosis. Have you checked for those conditions? Coccidiosis in particular can cause a B vitamin deficiency in your birds because the Cocci eat it all. If you have this, you would treat with Corid, then afterwards give them B vitamins (not during treatment, cause it will make treatment ineffective).
