I agree with Old Soul...teach her critical thinking. As JWs we never learned it ourself, but maybe you can find some books her age level to start with. When she learns critical thinking in life situations, she'll apply it to the JWs and see all the false reasoning, strawmen, circular reasoning, etc.
Also, very importantly, show her unconditional love.
Try not to attack the JW religion but just get her to reason on why she believes something. Otherwise, she'll learn to build fences around her religion and her thinking and won't let you in.
Good luck.
Joy