I would be concerned. It sounds extremely controlling.
Obviously you can't go back in time, but I wouldn't see staying in contact with her as rubbing anything in. It's just maintaining a relationship. Being isolated makes people more vulnerable. I'd want to change that going forward.
If she's been struggling with the fertility, I can see how any explanation would be something she'd be more likely to grasp at. The fervour of what you describe would make me concerned st how much pressure and manipulation had been going on from behind closed doors from BIL.
Criticising, or seeming to be critical, of the path she's on will likely just make her more defensive and shut you out. All you can really do, I think is stay part of her life, so her social contact doesn't narrow so much the only influences in her life are from within that one limited circle.
If you're worried, rather than giving her your own opinions, ask her questions that will get her thinking or give her the opportunity to share with you her own views. Sow the seeds of alternative views, and leave a way open if she changes her mind later so she won't feel embarrassed or isolate if she wants to pull back on .
All of that said, it might just be that this is how she's coping with what she's been through, and it's providing a source of comfort.
But the email thing would set alarm bells ringing for me. Religion as an excuse to control your wife.
You might find the advice here helpful: www.womensaid.org.uk/the-survivors-handbook/im-worried-about-someone-else/
Basically, don't pass judgement, don't tell her what to do, don't let yourself get cut out, be there for her as a supportive and non judgemental presence in her life. Think about the ways you can share your life with her without it all being about children. Trying to "hide" that side of your life from her might actually be emphasising to her that it hasn't worked out for her.
Oh, and as for visits, could you see if there's somewhere local where she could worship while visiting and pass on the details? If that's not the real reason you'd then have a better indication of how things are, and it would be an opportunity to reinforce to her that you love her as she is. (Important if she's got people/BIL in her ear suggesting otherwise.)