How about backing AND binding in the sky blue.
Use a great quilting design that will allow the back to 'read' like an interesting whole cloth quilt.
This way she gets 2 quilts for one!

Jan in VA

Being close to the memorial holidays, there are a lot of red-white-blue fabrics out there. What about a white background fabric with r-w-b stars peppered throughout? You could use the backing fabric to bind the front border, which would introduce the back nicely.

I just googled "red, white, and blue fabric" and came up with many that I think would complement your lovely quilt.