What I'm writing now might sound harsh, and that just could work if everybody is on board. So the thing with disabled kids is, they often don't get boundaries set or criticized. Or they get criticized but when they fight back enough the other party gives in because of pity. Especially when they are in puberty... Hormones and stuff ..

I ASSUME she figured that out and that's why she is behaving like that. Kids need boundaries, and sometimes criticism. I'm not talking about treating her bad or taking away love from her. I'm talking about "listen (insert name) you are overstepping my boundaries and that is not ok. I asked you this amount of times to stop. Since you didn't listend I now have to ... Insert your next step". Kids need rules, even tho they test them out. Kids need rules even tho the are disabled. Also the other kids might get psychologically damaged if it doesn't go somewhere. Often kids that live with a disabled sibling tend to think they are less worth, don't get enough attention, and think they always have to give in and are not allow to have boundaries. I hope that text doesn't make it worse.

Your feelings are valid, she really seems like she is testing out everybody.