Strawberry, If you haven't read Steven Hassen's books then I would suggest you do that so you know what to and what not to say. I agree with the others that you should keep away from discussing religion. I would continue to do what you are doing so you can have some type of relationship with her.
My husband told his mom who is in her mid 80's and has been in since she was a little girl that he no longer believed it was the "truth". He told her that if she asked him questions he was going to tell her the truth and if she talked about her religion then he had the right to talk about how he felt. She has not shunned him but their relationship has changed. She never brings up the religion so therefore he never talks about the lies of the WTS.
There are ways to get around not answering her directly and use the reverse of their "theocratic warefare". I would have no problem not answering her or changing the subject. I liked what someone else wrote that they are the apostates according to their definition because of all of their false teachings, so you aren't reading the WT and Awake so you aren't reading apostate books and magazines.
I hope it all works out for you and you can resume some kind of a relationship with her.