I do as Jingle says. I make shams with a zipper or velcro closure on the back. There are a couple of problems with pieced pillow cases besides the fading as mentioned by Mkotch. One is that if it's not layered and quilted the raw edges will fray out in the wash. Another is that if you put your face against the pieced area you might feel the seams. Simple is just better in a pillow case. If your sister is saying "pillow cases" maybe she means that literally and you could just make pillow cases from one or two of the fabrics to coordinate with the quilt.