You could get something in a rectangular cut. Have her unzip the top part and use it as a quilt (zipper down). Need more cooling keep unzipping. Maybe this?: http://www.rei.com/product/846256/rei-siesta-25-sleeping-bag ... though its only rated to 25°F

Sounds an awful lot like a quilt.... you could get her a quilt! Enlightened Equipment has a 20°F rated short-wide prodigy-X quilt for $185: http://www.enlightenedequipment.com/?product=prodigyx-20-2