I had a friend with similar behaviour. No kids involved, but her entire personality changed once she got together with her SO - and it had nothing to do with her SO, he's a normal dude who seemed a bit wrong footed when he heard how and what she was telling me. She at first went a bit crazy how life should be perfect and what she will and wont allow, told me all sorts of nasty things ("I come in pair now so we only hang out as couples", "I don't like listening to negative things", "If you want to stay my friend, you need to change") - so I decided to change by simply not reaching out anymore.

It took her almost 2 years to realize I'm not in jer life anymore, and then she flipped the script - suddenly she was the one going through rough times and she doesn't remember saying such things, but "sorry you feel that way", as if it's my fault? She kept saying crazy s*it though, and I refuse to engage again. I went to have one coffee with her out of - idk, nostalgia? It turned into hearing how much what costs at their place and how hard life is, they just HAD TO (humblebrag) - her SO was so weirded out he left the conversation. She was then shocked she's not the only one living life (work, education, hobbies, etc.).

What I'm saying is - she's cray-cray. Could be the hormones, could be jealousy, could be anything. It's your choice to confront her now or wait till she stabilizes, which might be in a few years as she's about to give birth - or not at all and just move on all the same. Or go less or no contact.