Asiablue, if you usually do send a card, and part of you wants to, perhaps you could find a low key one that just says "Happy Mother's Day" and write something like "Hope you have a great day" inside? Nothing gushing about 'world's best mum' etc?

I am not for one tiny second saying you ought to send one - just if it would be a gesture that would make YOU feel happier? I mean, I'm not bothered about not sending one because we're crap at cards in my family anyway so it doesn't really matter (though I will be sad not to speak to her on the day, I doubt she'll even notice) but if cards are something that you like to do, or have significance in the wider context of your relationship, might be worth considering?