SP, It's all her choice how she wants to spend Mother's Day. I understand it's not normal or what you want. Her choice, choices have costs let her own it. It's just a day on the calender, Mothers Day is celebrated on different days all around the world. Let your kids pick a alternative day if they want.
Cheers
ps Love the Major Kong quote.
M22,H45,W45 S21/18D12 Retain faith that you will prevail in the end, regardless of the difficulties and at the same time confront the most brutal facts of your current reality, whatever they might be.