So, I raise meat birds as well as pet eggers. There was a 4-5 lb meat bird (much smaller than the rest of the flock, but not a runt) who had been mated by the rooster(s) to such an extent that it removed the entirety of the skin on most of her back, the top portion of her rear, and extending down both flanks. Most of the damage was hidden by her feathers. Once I suspected something was up I took a look, and that's what I found - she had bloody gashes and partially healed scabs all over. Scabs were full of dirt and who knows what, but were solid. If I'd known sooner what was up with her, I'd have stopped it, but I didn't know. She was walking around somewhat tenderly, but still quite active and eating just fine. I put her in an isolation cage for a month, and then put her with a hen only flock for a few more months. By then most of the damage had healed, skin at the edges of the scabs looked really healthy, and most of the scabbing had healed over, and scabs were starting to pop off. She stopped laying for a month or so, but that was it. She went back to laying while still having massive scabbing. I think the damage would have healed completely in 4-6 months. Feathers were even re-growing.
When she was first injured I considered processing her due to pain, but she seemed to be moving around and eating and drinking fine. After being in isolation for just a week, she had perked up significantly. I didn't put any medicine on her wounds at all, just isolation. I was going to put some Neosporin, but by the time I found the tube, she had scabbed up, so I just left her alone.
Had another hen with a 1" hole in the back of her neck from a chicken-on-chicken attack, where you could see neck muscle, and the wound moved and opened whenever the chicken moved her head. I isolated her, sprayed the wound with Vetericyn as it was a fresh wound and I thought that might do some good, clean out any contaminants. She seemed in pain/depressed when I found her but was still eating/drinking. She perked up in a few days and was back to normal activity. Over the course of a month it healed up so well you can barely even see a scar, and all the feathers grew back.
I say all this to say, don't stress about the medicine too much, what type and how often to apply. I've had several wounded chickens heal up just fine without any at all. Neosporin or Vetericyn are helpful. if you have medical skills to help the wound, or can do stitches or something, and are able to provide medical care, have at it. But chickens are amazingly resilient and can heal on their own from many things that if they were people or dogs I'd be a lot more concerned about.
You can always give her time and see how she does. Of course she's in pain, but it's really up to you whether you think it's too much pain and it's time to end things. As long as she's walking about and eating and drinking by herself, I'd give her a chance to recover. Give her a few days to a week and see if she perks up a bit. Don't be surprised if it takes about 6 months to fully heal. Now, if she was in poor health to start with, or it looked like she wouldn't make a full recovery, then I'd consider end of life options.