For me, this has nothing to do with religion and everything to do with the typical issues of bringing a potentially uninterested SO to the gaming table.
The first question to ask her, when she's alone, is "Why do you want to play?" Listen very, very carefully to her answer. If one of the first two answers is because she likes something about the game (story, RP, exploration, imaginary killing, tactics), then you'll be fine. If one of the first two answers hints at "Because I want to check up on my boyfriend" or "Because I want to do everything my boyfriend does, even if I don't think I'll like it" then you've got a potential problem. If the first two reasons are both that she likes something about the game and she has separation issues with her SO, well, hope for the best.
I can tell you that I've had players who were at the gaming table for the wrong reasons. It's never worked out badly, but it's never worked out well. (Usually, we just get stuck with an NPC after 1-3 sessions.)
I've NEVER had someone give an existing table an ultimatum on how to play the game with them. That takes some serious stones. It's a very bad warning sign.
I hate to say it, but it sounds like there's some control issues in that relationship that are going to get worked out through you. In fact, no matter what you do, you may end up losing a friend. I hope I'm wrong, but...
Now, I have to ask: what happens if her character dies? Are you going to fudge the rolls to avoid that?