How do you deal with a person like this? (details)

My mom is really childish. Like on Easter, we were supposed to make coffee at church for the brunch in between services. But we forgot what time the first service was, so we got there just as it was starting instead of a half hour early. Somebody had made the coffee. My mom yelled at the person who’d done this because it was her job. The same thing kind of happens at every single Thanksgiving and Christmas – she gets told what food to bring, and she acts like she’s the little kid who didn’t get the part in the Christmas play that they wanted. I almost always apologizing as we’re leaving, or end up sending people messages on Facebook/email to apologize. I know I really don’t need to, but she’s not going to apologize, and I feel like somebody should. It’s one thing at home where it’s just us, but with relatives and friends, it’s awkward and kind of mean of my mom to ruin everything.

P.S. Sorry about the long read…