Maybe this will help:
Have your family member read Acts 1 and Isaiah 43.
Ask who is speaking in each chapter. Is there a command that we should follow? The answer should be "no". Then ask by whose authority do you call yourself one of Jehovah's Witnesses if there is no scriptural command to do so?
Next, read Romans 10 and Matthew 11.
Again, ask who is speaking and what instruction has been given in each chapter? If she hasn't applied this instruction, ask by whose authority has she rejected it and why?