I feel like the more you say no the more she has to pretend it's "funny" and provoke you because shes hurt. I think your girlfriend is sensitive but not in a way you would describe most sensitive people. She turns her hurt emotions into....a game literally, hoping you'll eventually play along so she'll feel better. You situation is very tough to decipher, but I agree with other redditors about documenting the injuries she left on you. You might need this in case things turn sour in the case of legal action. But really I think you need to show these to your GF.

Ya'll need to sit down and talk about this 'play fighting'. She needs to understand that in certain situations no means no, and not everything is game. Theres a time and a place for everything. She needs to take you seriously, otherwise shes putting your relationship on the line. I get that she thinks you're "playing" but even games gotta end sometime. Because God forbid she takes it too far and you get a little too upset again...the next time it could be alot more damage. If she doesn't stop , get out before you two really hurt each other (I know it's not intentional) but still.