Hello, I just started raising backyard chickens back in August. Everything has been great up until 3 weeks ago my son’s dog attacked Penny. We immediately removed her from the flock and have been nursing her back to health. She seems to be doing great now. I have tried 2 times to put her back with flock and one of the other chickens keeps attacking her and pecking the feathers on the back of her neck. There are no visible injuries there. Only on chicken starts this behavior but then they all seem to pile on. Any suggestions?