my mentally challenged sister's need to "protect me" has ruined my whole life.

all she does is just agree with everything someone else has said, for the sole reason that they said so. which is a problem for me when it comes to conflict in my life because she always feels the need to "defend me" which consists of talking over me non stop and refusing to let me get a single word out. so what happens is that whenever I'm in a conflict with someone, the person I'm in conflict with will tell my sister "my side" which is always either purposefully misconstrued or outright made up to fit their own narrative. and what happens when you combine these two issues together, is that she tries to argue for me by talking over me non stop repeating which they told her my narrative is. and as a result of all of this, they just end up believing that whatever they knowing made up or misconstrued "ended up being true anyways".