If the bullied hen is injured then separate her in order to let her heal. Otherwise, what you do is you separate the bully. Keep her out of sight for about 3 days. When you return her she will no longer be at the top of the pecking order and, hopefully, it will stay that way. Adding older hens to a group of young ones is a recipe for flock dynamic issues, but I have done it numerous times. I have suggestions about how to make it go easier in this FAQ:http://hencam.com/faq/introducing-new-hens/