Snipped for brevity. The religion was strong in her, and the control - in him. IMHO, BM would be controlling his family, finances, everything - even if staunch atheist. But his conservative, parochial views probably further contributed to the family dynamic. P.S. SM’s parents were from the same religious background, but her father sounded like a totally different man than BM.
My very personal suspicion, but I think that SM’s outlook on life was mostly affected by her getting cancer at such a young age. This is why her marriage with BM imploded so late; given how different they were, they should have divorced much sooner. But maybe she felt she was given a life, and a family, for a reason, and stayed with that family, no matter what?