This is not your fault. Even if someone got more love, someone else still could be accepting and compassionate. You suffered the smothering of your mother's love if your situation is like others I know. Your sister needs to stop hurting others and find someone to help her deal with her inner pain and anger. Unless she asks you to help her, in which case you could suggest a therapist, you probably can do nothing except protect yourself and keep yourself well. And be a compassionate human being.