Wendy,
I'm sorry that you feel that your mother is lost to you right now. As you say, you have nothing to lose by continuing. However, the very fact that she is open to discussing your points could mean that she has unanswered questions about her faith. You are the only person that she can talk to about them, as you know it's out of bounds with other JW's.
We've recently started to think that we may eventually get through to my husband's JW mother. I thought that this would make me feel elated, but as you say the thought of her having to admit that she's dedicated her life to a fraudulent religion is upsetting. Meanwhile, though, she's wrestling with the guilt of never measuring up to 'Jehovah's' standards and is alienated from her family. She hasn't seen much evidence of the promised love and support recently. So which is worse?
I just wanted to say hang in there. You might get your mum back one day. How could she resist a great daughter like you. I just hope that she sees the light for your sake.
Love
Sunbeam
xxx