After my chicks turned about 3 three months old one of what I thought was a leghorn hen was being beat up and could hardly walk much less socialize with the rest of the flock, I took her out and kept her alone for at least a month while she healed and once she was doing better I introduced her back into the flock by putting her in the coop at night after the others had settled down for the night then took her out in the morning. After about a week of this, I finally left her with the others and all turned out fine.
Now I now that she was actually a slow developing roo and what was happening was that the other roo's were fighting him, once he was healthy again there was been no issue and he is almost at the top of the pecking order.
If you have a sick or hurt chicken, get it away from the rest; chickens can be cruel and they won't stop picking esp if the hurt one can't get awya or defend themselves.