Partner’s mother refuses to accept me. What do I do?

Tldr: my (28F) partner(32M)’s mom (60sF) HATES me because I’m not of her same faith, what can I do to get this frustration out (without letting her know how I feel)?

Context: My partner and I got pregnant around 9 months of dating. I had met his parents thrice before we told them I was pregnant. While I was pregnant, it slipped that I’m not Christian. My partner didn’t want me to say anything because his parents are… yeesh. Insanely bigoted towards anyone who is not a perfect Christian.

Anyways, we’ve been together 4 years now, our lovely baby is a whopping 2.75 years old now. We took a break last year for a few months. I think with us moving so fast in our relationship, it stunted our ability to communicate and grow with each other. However, after our break things have been so much more respectful and understanding on both parts. I’m glad it happened. When we told his mom we were back together, she said, in front of my boyfriend, that I was more Christlike than most people of her religion, she missed me terribly, blah blah blah. The very second we got alone she said she was “very disappointed” that her son “chose someone who will never know their heavenly father.”

While we were apart, she threatened a medical POA over my son because she was afraid I’d miss his appointments. She said, and this is verbatim, “I could get one because you and [my boyfriend] were never married.” I told her “its still fraud whethet or not we were married, and I’m liable to sue, but do whatever you feel is right.” Then, she led me to believe that my then-ex was OK with her having medical POA and that she was going to pursue that. Turns out, she asked my boyfriend what he “thought about it” and he said it was unnecessary for her to have POA. He had no idea she threatened me that way until we got back together.

She told my boyfriend today that she doesnt think I am bathing our son enough because my boyfriend brought him over to her house with dirty soles one time (he’s 2? Kids get dirty feet idk. Its not like dirt was caked on or his feet had any block spots?). When my son was just an infant, she came to visit and I didnt notice my son had a poopy diaper because they were holding him while I was doing dishes. His mom and dad both spoke to him about how they’re worried I’m neglecting my son.

I could go on. These are the most egregious behaviors she’s displayed (besides the one time she cornered me in a fast food chain, and spoke for an hour about how I should convert, not realizing that I couldn’t see her at all. I had lost 85% of my vision due to hypertensive ocular migraines, most likely induced by her bs). I’m at a loss. Normally I’m fine with people who don’t like me for whatever reason, I’m not shy to that. However, I’ve never dealt with someone who actively tries to sabotage me, even when I’ve made it clear I’m not out for war. I just want to be nice when our paths happen to cross, and otherwise leave each other alone. I could go my whole life without ever muttering her name again. Lmao

Anyways, what can I do? I’ve written letters I’d NEVER send, letters I’d like to send (but don’t because i’m letting my boyfriend practice placing boundaries with them), even letters of forgiveness. I don’t go to their house anymore. If I see them around our small town, I greyrock like its going to save my life. But I still feel frustrated, and I just want to let go of it.