I'll link your duplicate thread. Some interesting comments there.
https://www.backyardchickens.com/threads/chicken-violence.1654761/
Different things could be going on. I'll present my theory. The injured hen may have been the dominant hen for those five years but is getting old. Another hen saw her chance and defeated her to become the dominant hen. When a dominant hen is cast out of office she sometimes becomes a bit of an outcast. By being beaten she has shown to have a weakness. Chickens can be bullies.
Another theory. She could have been the one challenging the dominant hen and was injured in the fighting. She lost and, well, chickens can be bullies.
I don't know that my theories are any better than anyone else's. Keep her out until her comb is healed and try to reintegrate her. If your reintegration is unsuccessful I'd rehome her.
https://www.backyardchickens.com/threads/chicken-violence.1654761/
Does anyone know why a peaceful flock would all of a sudden have a violence outbreak? Is this fixable? Will I need to rehome the troubled hen?
Different things could be going on. I'll present my theory. The injured hen may have been the dominant hen for those five years but is getting old. Another hen saw her chance and defeated her to become the dominant hen. When a dominant hen is cast out of office she sometimes becomes a bit of an outcast. By being beaten she has shown to have a weakness. Chickens can be bullies.
Another theory. She could have been the one challenging the dominant hen and was injured in the fighting. She lost and, well, chickens can be bullies.
I don't know that my theories are any better than anyone else's. Keep her out until her comb is healed and try to reintegrate her. If your reintegration is unsuccessful I'd rehome her.