You’re not overreacting. It’s weird she wanted to be in the delivery room in the first place. She needs to apologize and start treating you differently if she expects you to let her watch your kid.
This has all been dragged out for too long now. You can have whoever you want at your birth, no questions asked. I can understand her wanting to be there but I don’t think anyone apart from the dad should have an expectation to be there. (If she’s only got sons I wonder if she felt this was her only chance to be part of it?) But those are her feelings to manage and she shouldn’t have put that on you. Are you welcoming when she does come to visit? Do your fil &bil make a lot of effort with the baby? Have they seen him a lot more than mil? I think the point where you felt you wanted to stop sharing pictures is the breaking point as you’re purposely doing that to get at her. (I get it) but before that you hadn’t purposely hurt her with the birth thing. But now it’s tit for tat 🫤 I think you need to have a conversation & to draw a line under this. It sounds like you got on pre-baby so seems a shame to completely cut her off. If she’s not willing to meet you part way then reassess
I would be expecting an apology as well if I were you, but it seems like she doesn’t see that she is wrong. I think in this case one of you two will need to give up to the good of the relationship as a family. Maybe if you just tell her you had no idea she would be upset for not been chosen and explain that was not a form of attack or anything and that you appreciate all the good things she had done for you during your pregnancy, she might calm down and realize that in the end it’s your decision in terms of who would be in the delivery room (I personally would not choose my mil at all since you are naked in that position 😂 let’s be honest). Just think about the big picture! I don’t know how old she is, but sometimes our moms generation see things in different ways