Let her know how much you appreciate everything she does.
From the heart.
When I worked at a nursing home, I once read a letter to one of the residents, from her grandson. He was probably in his late 20's.
It was a very simple letter, just about everyday things. At one point he wrote "Grandma, when I think back on all those potato pancakes you made for me, when you knew no one else liked them, I know how much you love me, and I love you."
Both of us started crying, it was just so sincere.
She said, as she wiped at her eyes with her dainty hanky "That boy surely loved those potato pancakes."