Many times it is not possible to evangelize a relative directly. Jesus himself pointed out that a prophet has no honor in his own country and among his own people and his own household (Mt 13:57). If she will not take religious literature and responds badly to religious discussions then the best thing you can do is pray for her and love her and refrain from doing things that antagonize her.
This does not mean that one should capitulate to Jehovah’s Witnesses sensibilities. I wouldn’t take a crucifix off my wall or anything like that. If she wants you to accept her the way she is, she needs to accept you the way you are. Be a loving Catholic role model for her, pray, and by God’s grace things may turn around.
Regarding her soul, there may well be danger there. We cannot see her heart, and what you should do is simply be a loving brother for her and entrust the care of her soul to God. He works miracles.