You could do what I do whenever I'm supposed to do anything with Mr. KR's family and come down with the flu. I find its very effective! :)

Best of luck whatever you decide!

Signed,
Been there, done that, got the t shirt

Last year one part of our family skipped out, saying they had been given tickets to the Pacers game two hours away in Indy.

Tell your mom that you won't be able to attend as you have plans for a SERIOUS hangover. :p

Seriously, just don't go. If you feel comfortable doing so, tell your mother that you have not enjoyed the previous brunches and that's why you've chosen not to attend. When she says, "Everyone loves the New Year's Day brunch!" just respond, "I don't."