It sounds like a spinal injury to me. It happened to a couple of my ducks when my dog stepped on them. They can be nursed carefully back to health as the previous poster suggested. It takes time.
I had a flock of seven hens ranging from two to six years. A hen who had been quite dominant suddenly started getting so picked on that she wouldn't come in the coop at night to roost. So I separated her. She had completely stopped laying although she'd been a regular before. She had a dirty...