The joy you must be feeling now, with your sister being open to discussion, must be wonderful. We know this is rather major. But you know, "feelings" are all so relative. I remember the great wonder of it all when I was a faithful JW. No one could sway me; I simply would not put myself into that position. I was "strong". But I discovered for myself that I was on the wrong path.
Only one person that I can remember attempted to sway me. He had the Crisis of Conscience book and had read it himself. The congregation was actually publicly warning us to stay away from him. He was a very nice person, and he was the husband of my sitter at the time. I was so terrified, that I wouldn't even "touch" the book. Of course, since then, I secretly got it from the library on two occasions to read prior to making my decision to walk away. Just a couple years ago, I read it again.
I know you don't want to take away your sister's joy and happiness. The most important thing is that you show love and compassion. If she sees for herself that you are happy with your choices, then she may begin to ask more questions. I have found personally, that it is best not to attack the belief system of another person. That is such a fragile thing. If they have doubts and questions, they just need to feel comfortable expressing themselves. As we know, the borg frowns on self-expression, unless it is their own repeated dogmatic views.
Remember, you cannot change another person. But, sometimes, when you let go, they want to grab hold of you and hold on. It's amazing how situations work out.