Dear Cognac,
I am in a similar situation with my mom as well. I was the last of my siblings to remain in the religion. I was the one she confided in spiritually to encourage her. Now I'm the worst out of all of them. It didn't matter that I never committed the same level of immorality as my siblings. It didn't matter that i was and still am the most responsible out of all of us.They left because they were weak in my mom's eyes. I left because i was full-blown apostate, not satisfied with the "truths" that i had been taught growing up. Now she doesn't shun me, but she is terrified of me and we always get into huge arguments that leave us not talking with each other for months on end. I never want to get into TTATT with her, but her guilt-tripping tactics drive me towards that topic.
It was a huge mistake to reveal my cards, and share what I learned with my mother. My other siblings learned TTATT as well, but they were smart enough to pretend ignorance to it. I'm not saying your mother would react the same way. No two mothers are exactly alike. But there is a very high probability that sharing TTATT will blow up in your face.
Please tread carefully.