Hello!
This was most likely a rooster trying to mate and the spurs or nails cut the thin skin.
First, Cut any remaining skin hanging off. Then, clean the wound. Seperate her, and give her some electrolytes or antibiotics.
Chicken's hearts beat 300 times a min. so they generate more blood, therefore the healing process is quicker then human, you should see it healing up within a few days. You might can stitch it up, but I have known a few people to just leave it be and it heal it self.
Just keep an eye on her.. she should be fine, I hope somone more knowledgable with this will chime in, and correct me if I am wrong or add to this.
Good luck!