You could stick a gift certificate in your card to her favorite restaurant or to her son's if you know it so they can go out and celebrate (again i'm sure).
Or anoter gift certificate in there for her to go somewhere and pamper herself since she has been stressed lately. Those are just my ideas if you wanted to put something in the card or mail it separately. I know some salon and spas here in town will gift wrap a giftcertificate and then mail it to the receiver's home for you.