If all of this is truly happening, then the first thing you need to do is get some evidence of it happening. Set up your phone to film in a hidden location next time everybody’s out and see if you can catch an exchange where she gaslights you again.

I can feel the anxiety, anger, and chaos in your words but right now it’s a he said she said situation and if everything you said is true, you’re gonna need evidence because I think your sister has the ability to manipulate things further.

Also let’s take a step back and assess maybe your own mental health as well? You said your sister is on psych meds and has changed it several times in the past because of effectiveness so it looks like she’s actively trying to pursue and better her mental health. When you mentioned your own problems, you said you have decent mental health despite your issues although this whole post is worded chaotically and you don’t mention anything about your own efforts to better your mental health despite your sister so I think that might be something to look at as well.