How to say no

I know my mother wants to be in the room with us but I feel like she can so easily ruin a moment for me. Her and I are NEVER on the same page, we argue a lot, and we just never had the mother daughter friendship. We are just different people with different personalities and COMPLETELY different ideas. I already told her yes but now that I’m 2 months away from delivering I just don’t want her in the room when I’m pushing. Is it bad to say I’d only want my boyfriend and my sister (to record)? I’d allow my mother in there for the beginning but once it’s time to push I’d like her to stay on the waiting room but now I don’t know how to tell her I’ve changed my mind without starting WWIII or hurting her feelings. On top of that I’m still living with her because we haven’t had the money to move out again so I’m really scared about having to deal with that attitude afterwards, please help! How do I even begin this conversation? I need some advice ASAP thank you so much!