Cast out hen

[Aprylb]

I have had 5 hens and a rooster for a few years now. This year I decided to add 4 new hens. They were integrated into the flock about 3 weeks ago and are just beginning to lay. The new babies are in their own coop but in the same run. All seemed well until 2 days ago. The entire flock (except the rooster) has turned on one hen (one of the originals) they chase her pin her down and violently peck her head. She isn't injured or sick. Why have the cast her out and how do I fix it?

 

[HappyClucker7]

You can try cutting some pine tar in the places where they peck her. Chickens hate the taste, and once they get a little in their mouths, they won't want to peck her anymore. If they still chase her, you can separate each of the attacking hens one by one for a few days, and then return them to the coop.