I have this going on too. Right now, the bully is on day 10 of jail. The victim is still getting harassed a little bit by two other hens (#2&3) and I'm afraid if I cull the bully, one of them might take over.
I have pinless peepers on the way for the bully. I thought I could buy them at TSC; I had to order online instead.
The victim spent a week in jail first, just to be left alone. She got a little more sure of herself, but not enough, IMO.
I'd really like to keep them all. This happened somewhat out of the blue in February. I have 6 hens and 1 rooster (he isn't doing anything to protect the victim), and they have 164 sf in the run, which has been enough space for a year and a half.
I've had a nagging feeling that if anyone has to go, it would be the victim. I don't think the bully would go after anyone else.