Responses

Have you asked her the reason?
Maybe you can get an answer and then do something about it, or maybe she wants to get your attention and asking her to talk could set a different path. But mostly it could make it less funny for her. If instead of "you are mean!" you say "Are you al right? Dos you have a bad day" as if you were judging her instead of behaving as someone weak, she can stop feeling as if she had the upperhand.
I wish you good luck.
My sister keeps being mean to me, what should I do, I'm so close to losing my mind
she doesn't listen when I tell her that she's hurting me