We recently added 3 birds to our flock of 25-30 week old Pullets. The new birds were 17 and 25 weeks old. At the advice of the hatchery where we buy our chickens we were told this shouldn't be a problem and kept the new birds in a run attached to the coop all day and let the existing birds go in to join them at night. There was the normal sorting of the pecking order over the next day or two and then I thought that everyone knew where they stood. Suddenly in the middle of the day, one of the new birds starting picking on another of the new birds. Until now they had been allies, sleeping together and walking around the yard together but one started pulling at the others tail feathers. I noticed it when I went out to check on them all and she was bleeding quite a lot and had only one remaining tail feather. I separated her, put her in a large ventilated box over night in the garage, and gave her the roam of a smaller 'staging area' that is attached to our main yard during the day but didn't have any of the other chickens in. We've sprayed her with Blu-Kote and have kept her separated again tonight. Any advice about how to manage this situation and get her back into the flock safely would be gratefully received. Thanks in advance.