Call her Marie. One way is to let a few other characters (Mike and John) express their frustration with Marie when she is not present; and actually laugh with each other by exaggerating and joking about her.
This is what we do IRL, rather than express any direct hostility toward the irritating person and create a real rift, we find some catharsis and release by laughing about how over the top and irritating she really is.
This creates an inside joke between two characters, one the reader is in on; so when Marie makes some otherwise mildly preachy observation, you can put a spotlight on it: Mike looks at John with a pained look and wide eyes, John bursts out laughing, and Marie is interrupted.
"Nothing," John said, "I was just remembering this stupid thing. Please, go on, Mike is dying to hear the rest of your story!"
"Oh, how sweet!" Marie said, turning to John, "I'm so glad you are interested!"
You can even use this as a step toward two strangers (Mike and John) bonding as friends. The only risk here, if you choose to realize it, is that Marie finds out they are making fun of her.
You don't have to let that happen, but if you choose to, you can handle that as a character growth opportunity for any of the three. For example, say John is actually a nice guy. Marie finds out they have been making fun of her, and retreats to cry. In his attempt to apologize, he learns her religion is adopted, and out of fear; it comforts her and makes her feel safe in an inherently unsafe world. Mike's attitude may be "She needs to get over it, the world is a dangerous place."
But John can develop sympathy for Marie, and become protective of her. His solution to avoid the religious talk is to talk to her about other things. Perhaps they even fall in love. Now they both have character arcs.