Issues with my mom

Struggling hard atm. I have been saying for months what my boundaries are and that I'm basically going into quarantine about a month before my due date. Everyone knows this and they all know my dd. So Saturday my mom just assumed I'd be watching my nephew on Halloween. I admit I yelled at her. I feel wrong for doing so. But I have been saying the same thing for months. And she still said but what about taking your oldest trick or treating? And your dad's surgery is scheduled for that day. I told her no. I tried to explain again.

Do I apologize for yelling and then just reiterate my point again to her and the exact date I won't be having other people around?

As for my nephew his dad my brother lives with my parents, and my fsil lives there and works from home so he has people that should be caring for him that aren't me. And I did not intend to take my oldest trick or treating. My sister, best friend or husband are taking her as none of them want me waking that far with my BP being so low and passing outs.