Yes, you should send her a card, along with a note saying something to the effect of "you probably don't remember me, but I met you a decade ago through your grandson, and very much admired you then for these reasons ____. While he and I didn't keep in touch, I've thought of you occasionally over the years, and each time it brought a smile to my face. I am saddened to hear that you are ill now, and wish for you a speedy recovery, or, if that is not to be, then I wish for you as little pain during the illness as possible." Even if she doesn't remember you, it might bring her joy to know that she positively touched your life.