Need help....

K my little sister has always been a loner. She's always ben different. She's always complained that she didn't have friends, that no one liked her, and we were always telling her that it was her own doing, that if she'd stop acting like she was 4 years old that she'd get more friends. But it has just now occured to me that it might have to do with our father, and that she might need serious counseling. And for about a year now she has been dressing totally dramatically, like she'll put blue in her hair, or wear really thick eyeliner or really dark makeup or wear all black and try to look all bad-ass, but she is just a little poser trying to be something she's not (note: I do not have anything against people looking like that, just when it's my twelve year old sister just trying to get attention, it's bugging me!!!!) But the thing that really worries me is that the other day, I noticed some cuts on her arm. I asked her about them, and she said that they were cat scratches. I know she was lying, because there was no way that they were from cats. I don't know what to do!!! I think she's started cutting. My 12 year old sister!!! I'm really scared. Can anyone tell me what to do?

Well, i thought about telling my mom, but that might just make everyone more miserable. And if I tried to talk to her, she wouldn't listen...... (I edited that poem by the way