Is this supposed to happen?

[chickengeorgeto]

Adding one bird, is very difficult. If you can separate her, do so, let her heal up a bit, then pick another bird of your flock to put with her. Now there will still be a bit of pecking, but it will be a one bird to one bird. After several days, then introduce the pair. When you introduce the pair, put the two bullies where you had the pair. This will allow them to work it out a bit without the tough pair adding their two cents.

Another thing to consider is your run, many are just an open rectangle. I prefer, some obstacles, some roosts, some platforms that birds can get on top or underneath. Some short walls in the middle, were a food bowl can be set up out of sight of the other food bowl. While your run will look more cluttered, it will actually give more space to the set up, and it allows lower birds to get out of sight to the more aggressive birds.

Chickens supposedly can only recognise about 100 different flock mates. This is what keeps large flocks from becoming a pecking, fighting, bloody, mess.

Do not create places where the dominant hens can trap the more submissive ones and lay on the punishment.

 

[aart]

https://www.backyardchickens.com/threads/chickens-wont-stop-pecking-new-bird.1194954/