There are viruses that can cause this. I've had several hens over the years with this strange affliction, and they never got better, only worse. In every case I had to euthanize them when they could no longer get about.
It's not possible to give you a diagnosis. But it's very unlikely she would respond to any treatment, although you can try an antibiotic. In my flock the likely culprit is avian leucosis since I discovered that from a necropsy on a rooster many years back. Unfortunately, a chicken needs to die to get a necropsy, but it will certainly tell you if you have a serious virus in your flock that could cause more of this.