I'm sorry you're having such a tough time about that incident. You owe it to yourself, your sister and other potential unsuspecting persons out there to tell your parents. Your sister sounds freakishly strong and mentally disturbed. Please don't be embarrassed. I'm sure you would have broken through if you were mad enough...you just didn't want to hurt a girl. She is abusive and I wouldn't put up with it for even one more moment. One of thes days, she's going to start stuff with the wrong person and it won't end pretty. She needs help. Please tell your parents so they can get her help. That or take karate or self defense. That would put an end to that really quick. Sending big hugs.