I agree, do not hang it. The best way to display a quilt that will not stress it is to place it on top of a spare bed in a room that does not get direct sunlight.
In this instance, I believe it would be well worth it to consult a professional. It's entirely possible that doing
anything to the quilt will reduce its value. I have never heard of any kind of spray that preserves fabric.
Quilt appraisers and repairers will be the best people to ask as far as how to best preserve and display the quilt. There are links at the bottom of the page of this website. Your friend should be able to find a professional near her.
http://www.quiltappraisers.org/