I'm so very sorry. It sounds like your mother is, indeed, a narcissist. Why don't they tell the truth? Why don't they say " My son is no longer going to jehovahs witness meetings so I am shunning , shunning my granddaughter, blocking his phone calls destroying his photos even his baby snaps. He is dead to me" and SEE how much sympathy she gets from non JW 's after THAT. My guess is you will be the one who gets the sympathy.
No women can loose "privileges" from talking to her faded son, so why do it (shun)? There is no where in the bible it tells her to do such a thing.