I hope by now that you have separated her from the rest of the flock, or she will not survive. My rooster’s days are numbered. He constantly jumps on the smallest hen, and he’s violent without romance.
So sad. Did your rooster do this? I've seen mine grab the back of the hen's head to hold her down and mate. I stop him when I see this. You may need to separate her from the others until she heals. I would put Neosporin on it to fight infection.