If I were in her position I'd ask that you DA'd yourself before I'd even consider reconnecting.
I think most people in your sisters position would be able to be aware that you were brainwashed and that the last thing you need is yet another relationship based on conditions. In my situation I think my sister could see that I was in a mess at that time and needed support. Her love was the best weapon she could possibly use to fight the wbts. As a result of it cousins who didn't know of one another's existence in the past, play together today.