Chickens are very resilient and heal from very serious wounds. It's good that you've cleaned the wound. If you haven't already, you should isolate her, ideally somewhere warm where you can keep a good eye on her. After an injury, chickens will go into shock, so it's important to keep her hydrated and body temperature up. If she won't drink on her own, you can try carefully dripping some water into her beak with an eye dropper or syringe without the needle. It's okay if she doesn't eat much for a few days, but you can try to tempt her with cooked scrambled eggs, yogurt, or feed with water. She'll be quite swollen so it might be hard for her to move her head to eat/drink normally.
Given the location and severity of the wound, you may also consider administering antibiotics. I found some at the feed store which I inject intramuscularly into the breast with an insulin syringe.
Best of luck to you and your girl!