Other than going with a 2 color quilt as many have suggested my only thought is, what if you showed her the pattern you want to use and explain that it just won't work with only 2 fabrics? Then if she won't go for it maybe ask her what sort of pattern she had in mind. Maybe she would come up with something you'd want to do?
I can understand the making most things for her idea. I got a gift card to a quilt shop last year and my hubby insisted that I buy toys for me with it, but the only "toy" I wanted was fabric to make my DS a quilt. Good luck finding a solution that makes you both happy! Happy quilting!