Its really to bad you dont have two coops. It is easier for adults to except another / or younger chicken into their group when they are no longer on their own turf. Thats what I do with them when I add more of them to the group. I geuss you could try to change the3ir enviroment in the coop. move waters and feeders around. Place tarps or boards around the bottom half of the wire so they cant see out. Do this at night. Then remove all of them from their roosts at night and put them out in the run. They will think they moved and their area is going to be different, so they wont be as upset when they see a chicken that is not in their group. I know this sounds crazy. BUt I have found that chickens are territoral and they do have the pecking order based on their own grounds. I have to different yards for the chickens. When I move them at night they dont where they are going, and then when they are in a different area they are more concerned about the new area than they are about the new chicken. It has worked for me. If you have another younger or laid back chicken I would put them together in a cage for a while and see if they buddy up. Dont be surprised that you will see them pecking each other , but it shouldnt be as bad, and shouldnt take as long for them to allow the new chicken in their pecking order. Any agian this probably sounds totally crazy but it has worked for me in the past