I had a chicken with the skin on her back pecked/pulled off my my ex-tom turkey
. Literally she was peeled down to the muscle, and her tail was ripped partially off, as it appears your chicken had happen
That was almost three months ago. I kept her wound covered with antibiotic salve and gauze until she formed a big, thick scab. Eventually, that fell off and she'd grown skin back. There is only a small spot, the size of a silver dollar, where the feathers have not grown back yet, but I see little nodules under the skin with tiny feather beginnings coming out of them. I still can't believe she lived, much less is normal. Chickens are tough, they can regenerate in amazing ways if you shelter them, make sure infection doesn't set it and give them time to heal.
I wish I'd taken pictures, but I was sure she wouldn't make it. Silly me.
Keep her inside and warm. The vet told me (for a duck) that a sick bird can lose 10% of their body weight per day trying to keep up their body temp while ill.
When I put my hen back outside, I covered her scab/unfeathered skin with Blu Kote (from the feedstore) so her sisters wouldn't peck at her wounds. Chickens will peck at red or pink things, but not dark blue ones