You can try putting a chicken saddle on her to protect her back and let the feathers regrow. Some hens will wear them, some are Houdini's at get out of them! How many hens do you have with this rooster? Sometimes even if a rooster has enough hens he will still have one or two that are favorites and they end up getting way to much attention. I have that problem here at the moment so my rooster is penned up separate from the hens for a while.
If it is more that the rooster is aggressive rather then just normal mating behavior then you'll have to decide if you want to keep him penned separate from them or if you want to get rid of him.