I know you feel this is embarrassing to you but you acted as the better person in this. What is really concerning here is that your sister has a huge issue and needs help. As others have pointed out here, who will she bully or even seriously injure next?

Please talk to a health professional, counselor or trusted adult about this. You need therapy for being hurt and your sister needs help. It might be that there is a mental health issue going on with her that needs attention!