I need help

Growing up i had issues with anxiety and depression. I take prozac and am relatively busy enough and have matured enough to find was of coping and moving around my illnesses. However, my sister has not. Shes almost 15 and on the brink of another big move, not only moving to another state, but also starting high school. She's had a TBI and has a hard time problem solving. She was taking medications that seemed to work relatively well, but it seems like all that has changed. She gets so angry and frustrated and sad, and recently we found out she is cutting again. I don't know how to help her. She doesn't want anything to do with me anymore. She doesn't want me or my mothers help. In her mind, we've become the enemies.. What do I do?