msiajw
Your sister is typical in not allowing herself to reason.
No one could have told me I was wrong, I would have argued for England and felt thoroughly proud of myself.
My guess is there will be possibly one issue that she has that troubles her. With me it was blood, my wife it was the love in the congregation, mother in law the static memorial partakers.
I tried to convince my wife the falseness of the WT by arguing the blood issue, this was useless because it wasn't an issue for her.
I say don't argue too strongly, she has to see it for herself.
It will be hard and a long road to take, but keep up hope that one day she will see it, just be there for her. My wife eventually came to to her senses. It is a great feeling.
Good luck