I'm somewhat ambivalent about Mother's Day. I appreciate a card, flowers and a meal out, which isn't on the actual day, it doesn't matter to me, some sort of acknowledgement is fine, I know they both tell me they love me fairly frequently that's what matters to me. My only thought is as a mother, never go head to head with the wife or partner, accept graciously, you are no longer the number one woman in your son/s life/ves, but you will always hopefully have a special place as his mother.
When my mother was still alive, I always sent a card and then took her out to lunch, for Mother's Day, but that was rarely on the actual day as my mum arranged her Sundays around going to mass.