Why was your sister pretending to cut herself? Was it for attention, or was she trying to piss off your mom?

Either way, hurting your sister won't solve anything. It sounds like she has serious respect issues and that she needs to learn how to respect others, especially members of her own family. However, I'm sure there's a reason for her behavior. (I'm not trying to justify her actions -- because I agree it's f***ed up -- but maybe there's an underlying issue that you're not aware of that needs to be addressed.)

Unfortunately, I can't offer any advice on how to teach her respect, but it's something you'll have to figure out. Maybe family therapy? No idea.

Sorry that your sister is behaving this way.