I'm going to slap a girl when I warned her twice that if she slapped me I would slap her back
Why would you hit a girl though?
I'll just fight back if she had slapped me first.
I can see you are in a difficult situation. You're in the right to defend yourself when you're being assaulted. If possible I would recommend not causing physical harm back to them and seeking help.
I don't think she's a good person and that she deserves to get hit.
If this continues I think you should get the authorities involved so it can be taken care of properly. If you decide to hit her back you could also be in trouble.