Should my parents take my little sister to a psychologist? How can I help her?

My sister has really bad attitude problems, and snaps at people in a really nasty way. She gets mad at everything and her anger turns really violent. Three days ago I was arguing with her and she stabbed me on the shoulder in front of my parents. We lied about what happened to the doctor. I told him I fell down... show more My sister has really bad attitude problems, and snaps at people in a really nasty way. She gets mad at everything and her anger turns really violent. Three days ago I was arguing with her and she stabbed me on the shoulder in front of my parents. We lied about what happened to the doctor. I told him I fell down while holding the fruit knife. She was crying and apologized to me. But I still think my parents should take her to a psychologist or something. My parents told me she was fine, that those are the hormones. She's 12 years old and I'm a 17 year old guy who have friends that are girls and when we where that age, they weren't violent at all. My sister is always angry. How can I help her?
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