Sounds like she wants a duvet instead of a quilt. See if what she has in mind is a cover for her down duvet; you could still make one for her and quilt the face of it without using batting. I've never heard of a batting being made with down.
Otherwise, suggest a wool batting - Hobbs and Quilters Dream both have wool batts - for fluff, warmth, and drape without heaviness.
Jan in VA