DON'T GIVE UP!!!
Although my r'ship with my JW sister has been strained at times, I have always let my niece know that I love her and as she's grown up, have always tried to stay in touch with her somehow. It can hurt sometimes, but if you make the effort, which may involve a bit of compromising around her parents, it can pay off.
Today we went shopping for her 16th birthday present. My niece hates the JWs as she can see that it's a cult, and she has even stood up to her mother on one occasion when she tried to stop us having contact. She has plans for the future and I am so proud of her.
So I can say from experience, if you make the effort, it can pay off!