I just had the same problem with a mean chicken. She started pecking feathers so I put her in another coop alone for a week. When I put her back with the others, she now started pecking all of them. So I put her away (out of sight this time) for another week. Integration was a bit fierce as others had climbed the pecking ladder and didn't like it when she immediately grabbed another chickens face and wouldn't let go. After a night pecking order drama and settling down, the next day she went right back to feather pecking.
Some feather pecking causes (low protein, boredom, over crowding) were all addressed and/or weren't issues.
I got rid of her the next day and everything has been calm since. I guess sometimes you just get a mean chicken. I didn't try pinless peepers and feel that maybe I should have before I culled her, but I didn't want to deal with her anymore. She was the head chicken and I had noticed from the beginning that she was a bully, so I wasn't so sure the pinless peepers were going to change her personality. I've read where people say they work. And I've also heard from people that said that the chicken went back to the bad behavior when they were taken off months later.
I don't know what to tell you, but it's nice to see my chickens' naked bums starting to grow feathers again.
