My hen Rosin was sick for a while and I had her separated from the others for a couple weeks, which caused problems. The others started attacking her when I put her back into the coop with them. They would get her cornered and just be merciless. So I tried placing her into a see-through cage for a time and let her out with the others when I could be there to control things (also to let her heal better first, since I heard that other chickens might attack a weakened one). I let her out as often as I could, letting the others chase her one by one (as long as they didn't get too rough) so they would feel less threatened by her presence. But after carefully watching them, I realized that I had one particular hen (Lobelia) who was more aggressive than the others and would lead the others to gang up on Rosin. Lobelia was a lot more serious about attacking Rosin and the others would join in when they saw her go for Rosin. So, this in mind, I took Lobelia out and put her in a section where she could see the others, but not be with them. I kept her away for a week, and during that time Rosin gradually got accepted by the others without Lobelia to interfere. When I saw that Rosin was comfortable with the others (about a week with them), I reintroduced Lobelia. It worked!!! Lobelia, while still occasionally going after Rosin, also went after a couple others, and I guess forgot that Rosin was THE ONE. Lobelia was much more settled down about things too, and now they are all one happy flock again, doing their normal things. I hope this helps anyone who has similar problems. I could be wrong and maybe it was just my particular hen, but it could be worth a try. I just observed like crazy and kept an eye on things for a while even after I thought everything was okay. Could be there's a ring leader or two in every flock that causes the rest to gang up - it was in my case - and the ring leader just needs time to chill out! Luckily the others didn't attack Lobelia when I put her back in with them, or that could have been a whole other problem! Okay - I'm done with my novel now! Hope this helps someone.