The only idea I have is to keep it light in weight as anyone who is going thru chemo is very sensitive to any kind of weight. I would not use any kind of foundation to sew the pieces together just sew them to each other like you do in regular piecing. I don't know why patterns call for a foundation, I very seldom use one. Also maybe if you backed it with flannel so it would be soft and feel like a hug. Good luck to you and bless you for doing this for her and good luck to your friend.