What are some things that she has created? Can you make copies/pictures of one or more of her works and create that image on fabric? As to warmth, I would back it with flannel and use either wool or polyester batting. Pure cottons for the top. If you want to add texture you can add extra batting in some areas, use old doilies, handkerchiefs, old buttons, appliqué, embroidery, etc. I don’t know what it’s called but the “new” thing seems to be joining pieces with crochet. Also you might think of fabrics that inspire memories. For instance, I’m finishing up a denim quilt that is made from my family’s used denim, concentrating on my Dad’s old jeans. Personally, I like keeping the quilting simple and somewhat minimal (compared to a lot of some I’ve seen) as I don’t like mine as stiff as a board. And I think the more quilting, the less warm they are.
Just some ideas that came to mind when reading your post. Hard to advise when we don’t know your sister.