My little sister regularly threatens to kill me?

So, me and my little sister live in the same house (we also share rooms) with my mom, dad and little brother. I’ve told her multiple times to be cleaner but she won’t. We often fight because of this. I do not know what’s wrong with her. And whenever we fight, she threatens to kill me with a knife. She’s tried to stab me multiple times but didn’t have the balls to do it. I told this to my mom (not my dad, because he is strict and could hurt her) and she told me it was my fault, and that I was just like my grandma. She tried to push me but I locked my door. Now they want me to open it but I’m too scared and frustrated to do anything. I need help.
My little sister regularly threatens to kill me?
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