When my polish looked like that from the other chickens brutally trying to murder her, I just used polysporin, warmth, and lots of tlc. Just babied her til she perked up and make sure eating and drinking remained normal. Shes finally got all her feathers back now except one bald spot on her head...
Water and salt. Put enough salt in so it dissolves. You can buy saline but it's easy enough to make! I put an electric fence up around my chickens and my chicken killerdog was kind enough to test it for me lol she says it works great
Keep her separate as long as you need to. Her being lonely is a lot better than an infection happening because she got pecked in the wound. Just keep doing what you're doing, applying the best first aid you can. Chickens can heal from some amazing circumstances you'd be surprised. And I'd be...