After measuring the pillow, I cut the fabric to size with a 1/2 inch seam allowance, plus 3/4 of an inch in the length for the no-sew velcro. 20 minutes later... Bunny got to try out a pillow.
Then another bunny tried out the pillow. She now carries it everywhere. For less than 50 cents, I made a pillowcase that matches Charlotte's bedding. And her size :)