Welcome to the site Ben! Thanks for sharing your story. It's good to hear that you and your spouse came out of the orginazation together. I feel for a lot of people on this site who can't speak honestly to their spouse for fear of being outed.
As for your mom, if you really want to be able to reach here I wouldn't recomend just comming out and telling her everything you learned. The WTBTS is pretty good at hardening people against so called apostacy. You have to be away for a little while to gain perspective. I would recomend assuming the Null Hypothesis when speaking to her (not convinced one way of the other about the JWs) and keep the burden of proof on her.
If she asks, "Why did you stop going to the meetings?" You can always say something along the lines of "To be perfectly honest, I'm not sure that I have good reasons anymore for believing the things I used to believe."
If she asks why you feel that way - you can follow up with a question of your choice.
My favorites are:
"How do we know the Governing Body is the Faithful and Discreet Slave?"
Or, "If sin entered into the world through Adam and Eve and death is the price of sin, then why do animals suffer and die?"
Or, "If man cannot rule over man and all badness in the world is being allowed right now to vindicate Jehovah's soverignty, then why did God interfere in the past with things like the flood, and the tower of babel, and all the biblical wars?"
Asking these sorts of questions is a good method to get the person to actually think instead of getting defensive. Inclusive questions are good too. When given an anwer you don't buy you can always say "Yeah, but how do we know that's true?" or, "How could anyone really know that?" or "I understand that's what you believe, but is it actually true?"
If asked a direct question its usually best to either say "You know, I really don't know." or, "I'm not sure anyone could know that."
Just do your best to keep the burden of proof on her. She's the one who thinks she has all the answers - not you. Its a good method to test the waters and if a few of these conversations go well then it might be good to start bringing up some of the things that you have learned. But I definitely wouldn't recomend an all out assualt on first conversation.
Hope that helps :)