Thanks everyone for your support. It means a lot.

@BirdDancer, I think you're right that she has some kind of personality disorder (most likely BPD in my opinion), but she refuses to see a mental health professional. I can't remember where I mentioned it, but basically, I mentioned a while back that my sister thinks EVERYONE ELSE should see a therapist. She thinks everyone else is the problem.

@~Christina: Yeah, my parents really need to stop helping her out. From my sister's perspective, there is no need to change her nasty behavior if everyone continues to help and support her. I don't even want to go to her graduation ceremony in May because she is so nasty, but I'm probably going to go anyway because it would hurt my parents' feelings if I don't go. So, I'm going because of my parents, not because of my sister.

@Innerzone: Yeah, I'm probably not going to go near her once her graduation ceremony is over with. (As mentioned to Christina, I'm only going because of my parents.) I've tried talking to her about her behavior and I've been giving her numerous chances to cut that sh_t out, but all she says is that OTHER people need to go to therapy. She refuses to go herself. I even asked her if she was willing to go, but she gave me a disgusted look and said, "f_ck no! I don't need it! so-and-so needs it!"

@Moose72: She has no friends besides her boyfriend. She doesn't understand why she doesn't have any. lol.