My friend has a horrible little sister, and she'd like to somehow get her to stop in a way that'd scare her or something but not cause her to tell her mom. Her mom won't help in this situation because she thinks the little sister is an angel or some shit. She can't just ignore her because of course, she's near a lot since they live under the same roof. My friend is younger than 18, so she can't move out but needs to get rid of this problem. I want revenge ideas, but if you have some helpful advice either than "ignore it" or "try to get out and away more or pass her away" or "talk to her(in a non threatening way" then I'm sure to listen.
Pic unrelated but I have no other one to use
how old is she? and how is she horrible
details pls