The bullying was taking place at night. She was keeping all the younger hens from using about two-thirds of the roost, with the result that about 14 pullets were roosting on top of each other in a corner. They have a vast amount of daytime space. So we put her in the Time Out cage at night (I hate calling it Chicken Jail, lol). She got released in the morning along with everyone else. But I also added another roost which probably also helped. For a couple of nights after that we had to go unstack the young ones and set them on the new roost until they figured out it was there. Chickens ain't rocket scientists.
If bullying is happening during the day, I would suspect the space is overpopulated. It can help to add hiding spaces for the victims to escape. If you can set up two pallets in an A-frame configuration to make an in-and-out so nobody can get trapped, that makes a good hidey-hole. Also things like kids' tables that they can jump on top of or run under, those are very good. I personally would not cage her during the day, it's too hot. Others might.