It's not unusual for mature hens to not allow a young rooster to mate. Some hens, especially young pullets, will squat for practically anything in spurs, but mature hens often expect a rooster to dance for them, bring them treats, be a guard, and maintain order in a flock. The rooster also has to WOW! her with his brilliance and personality. Many young roosters can't impress a mature hen enough to win her approval.
Another thing is that the mating act is an act of dominance. If the rooster can't dominate her with his personality, she is having nothing to do with him. I've seen hens go through the mating act with other hens when there is no dominant rooster in the flock so she can show she is the dominant flock member.
What is probably happening is that the rooster is big enough to try to force her, but not mature enough for her to cooperate or for him to dominate her spirit. She still wants to be top dog. It's probably an adolescent phase he is going through where his hormones are raging but he has not yet matured enough for the job. This stage can last months. He will probably outgrow it and learn to be dominate in his flock, but it is possible he could damage her in the meantime.
I don't know your set-up as to your options. Maybe you could separate them while she heals or maybe for a few months while he matures. You could get rid if either of them, but that is pretty drastic. You could let it go and watch for real serious damage, but if her comb is torn and such, that sounds serious enough to me. It is possible, not an absolute guarantee but a real possibility, that the other chickens will start pecking at the blood and injure or kill her.
This type of behavior is not unusual in a flock with mature hens and immature roosters, but I usually don't see physical damage. Usually the hen just whips his butt when he tries with them or maybe runs away, but the pullets cooperate.
