My bantam roo got his comb torn up by the big girls when he tried taking liberties
I didn't do anything for it and it healed nicely on it's own. Combs are very vascular and tend to bleed like stink, the bleeding helping to cleanse the wound and prevent infection. I'd just keep an eye on her, watch for any signs of infection or change in behavior.
edited--are you sure the biter is a hen? Just sayin'