I agree with nugget here. I think you need some distance from yourself and your mother. She's needs time to calm down,and you need time to figure things out,and just a break from her.
My mother wasn't this extreme,but she really tried to put the guilt trip on me,saying she just wanted to die. And then,she said,some people are just selfish,I know she was speaking about me. I just ignored her.
But,I did try to reason with her from my point of view. I was miserable being in this religion,and how is it selfish of me to just want to live my life.
I think your mother needs time. Hopefully,she will calm down. At the very least,I wouldn't discuss doctrine or the religion at all with her. You may have been thinking of leaving for quite some time now. But,this is all new to her,and she needs some time for it to sink in.
Take this time to enjoy your wife and kids.