A lapquilt with a signature block expressing love and appreciation is a wonderful gift to someone so important. I've seen relatives embrace lapquilts from charitable strangers while terminal. Now, imagine what it would mean from a loved one.
And, don't forget to tell her *now* how much you appreciate her and what a positive influence she's been on your life.
Bless you for thinking of her. Foster parenting can be difficult. We often hear very little about the positives.