It can be normal for them to attack and peck if she has been separated for a couple of weeks. Did you separate her in a wire crate within site of the flock? What breeds are your chickens? Do you notice any one of them being more aggressive? Sometimes you may have to separate or rehome a bully, or even the one being bullied. I had a hen once have an illness where she didn’t walk for over a month. Once she was again walking, even the lowest in rank bantam hen would jump her. I had ro separte her in the adjacent yard where rhey could all see one another between the netting. Months later, I put her back without too many problems.
I guess I can try to pinpoint the bully....
