I'm sorry Mother's Day is so difficult for you. I think Hallmark has made it very hard for many people. I never liked the sentimental, gushy cards though I loved my mother. I wish my mother were alive now so that I could just be with her.
I've never sent my T a Mother's Day card, but I recently took a photograph that I think she will like, and I might email it to her with a note. She loves her kids very much, so I think she will appreciate it. She will probably get a zillion wishes on Facebook from friends and relatives, but I know she will like my thoughts too.
I think your T will appreciate the card very much!