i would separate her asap, and not re-introduce til all bloody bits have healed up, or it will carry on. do they have enough space? unless she was a valuable breeding hen, i personally would cull her if u cant find a solution.
iv had a few problems this week aswell, our youngsters from last year are now maturing and think spring is in the air. a large young cockeral tried to mate with a smaller breed of hen and ripped off her neck skin in his enthusiasm, shes quite a mess but im hoping she'l pull through. and our resident cockeral has been beaten up, so had to separate and change things around. the larger young cockeral is now out with the the sussex hens, who are mucher larger and robust, and will kick his toosh if he misbehaves.
our rare breed poultry sale isnt til may so will try and keep peace til then!!