It's surprising how strong some girls are.
A girl, who was my friend, once slammed her fist down on my shoulder, while I was sitting because I was teasing her friend.
It hurt enough to make me mad but I kept my composure because I was in a room full of people, and she was my friend.
Looking at her expression immediately after I could tell that she was sorry and a bit shocked. It was almost as if she didn't know that she was strong enough to make a guy mad by hitting him.
So the woman in the OP might not be aware that she is punching too hard, she probably thinks that because she's a girl and you're a guy, nothing she does can hurt you.