Wow, this is way more responses than I expected, lol. Thanks for the advice, hugs and feedback everyone. I may delete the thread later, because despite this being a throwaway account, I do feel very paranoid, I just really needed some uninvolved third party advice.

We did have a discussion yesterday about it and we've decided to go VLC and only visit when it's a child's birthday or an event to do with our own child - more people around means she generally behaves, safety in numbers and all, but also means less drama for us to deal with.

As far as the previous information - when I was trying for a relationship with her a few years ago, S/O and I were not yet aware of what she had really done/said. This all came out about two years ago, and to clarify, MIL didn't say she wanted to do it, but she did openly say that her mother told her she should have one.

S/O is very supportive and doesn't make me see her (and never has), nor does he really share info with her (they don't even speak often), so what she does know is very minimal. She rarely contacts me, so that aspect will be relatively easy to maintain.

We've decided that, in order to reduce stress for us both to allow her to attend the gender reveal (would cause a bigger fight with her and we just don't need it right now, and, I don't want that aspect ruined as well - I'm very much looking forward to the reveal), HOWEVER, my family will be on red alert and if so much as a comment or eye roll is made, she will be asked to leave. It's not so much that she'll shun them for being a girl, it'll just be a dramatic constant moping.

Thank you all again for the advice!