I have been dealing with this for a couple of weeks... I took my chicken to the vet a week and a half ago. This is what he said...
He gave her a steroid thinking maybe she was injured (I disagreed) I asked for worming meds as we found eggs in her stool. So we wormed her and I keep her separate from the flock in her own cage snuggled around with towels and move her a lot for leg circulation. I began to dropper feed her to get more nutrients if the worms wiped her out. I hope you can get her nutrients up asap. I have been taking my chicken to work everyday to feed her and make sure she has not fallen over and gotten stuck.
I hope you have a different situation but I wanted to share just in case.
My girl seems to be getting a little leg strength back as I hold her up and feel it. If my little one doesn't get better by Monday.. or at least be able to be on her own I have chosen to put her down.
I have a friend who had a lot of time and her chicken recovered.... get her healthy early! and I am wishing you the best!!!! Good Luck and stay positive!