I struggle terribly with proper quilt sizes. There should be some kind of standard drop! However, as others have mentioned, dimensions of a queen mattress is 60 x 80 so at best, 72 x 90 would only give you a 5-6" drop on either side, and most mattresses are deeper than that.
I've never had too much shrinkage though I prewash everything I quilt. Maybe you could somehow add a border if she is unhappy?