I think my sister's insane..

I really think my little sister is insane, she's fucking 10 years old. 
So I was trying to make chicken soup to help with my cramps and it's seems my sister was about to cut up her pizza which I taught her how to safely use. 
I had my back towards her and I felt something poke my back, so I stepped backwards and it pinched. I turned around and my sister had the kitchen knife touching me. 
I told my parents about it and they didn't do much but scold her softly. 
I am actually fearing for my life as I tell my husband this. 
Note: my sister has hallucinations about cloaked black figures following her and the room become bigger when she gets sick.