I'm sorry to hear of your frustrations, azaria.
There could be another deep-seated reason why your mom goes 'confused' and 'talks over' you, not wanting to follow through on a conversation. I take it she was a convert, right?
I found this from a book on the old WCG and how it radically changed. The author (J. M. Feazell) makes this astute observation about ones who found it extremely painful to change their view:
Many, if not most, first generation Sabbatarians are Sabbatarians because they left a non-Sabbatarian church, with all the resulting social and familial trauma, convinced after much study that the Sabbatarian position was correct. They had suffered for the truth, and God had honored their faithfulness.
To reject these doctrines now would be, in a very real sense, to declare that one had acted foolishly, not faithfully. It would be to abandon their sense of having done something special, something extraordinary for God. It would mean that they were not, after all, one of the only people who were not deceived. In fact, it would mean that they were actually among those who were even more deceived than others.
Some minds are not ready to contemplate that agonizing truth. The fact that she said that if JWs aren't right, she'd stop believing in God means (I think) that she senses how traumatic it'll be to face up to what you're saying. Please continue being patient and loving with her.