You're one cool cookie kw,
At least your mum and you can talk about this stuff. I gave up trying to talk with my mum when I was about 12 (it's like we really are on different planets - hers only has Elders and a King James Bible).
Don't fret young fella. It won't hurt to let the subject drop a while. Just keep loving her. Make cups of tea for her and little things like that. Unexpected kindnesses are more powerful than any watchtower crap. You only get one mum even if she does believe silly stuff.
Live in hope, love ya mum no matter what. In the long run blood really is thicker than water.
Now get some rest! unc. (I'm in a really bossy mood tonight .. it's like I'm possesed by my mum