I am looking for a movie based on horror or thriller?

I'll explain it the best I can, The movie is based on a little girl who kills anyone, first it was her grandma, then went to a teacher and so on, what happened is her grandma is abusing her because she pushed the grandpa down the stairs then she pushes her grandma down a cliff and then she fakes that if she is okay but she really doesn't like her. Then the teacher from her school tries to expel her from the school but she goes to her place to send her a cake that has peanuts in it, she is allergic to peanuts and the little girl hides her thing what ever it is in the couch.

If you are not sure what this movie, show, series, or tv show then you don't need to answer the question. I looked all over the internet and I cannot figure the character name, I think it's Sadie? Not 100% sure. I just cannot find the name of it.