Better check what kind of elastic she bought also. The white stuff an go in a casing or you can stretch it and sew through it with a zig zag stitch. I am not sure how to work with the new fancy clear elastic. You might want to mark the circle on a square of fabric, sew on a separate long strip of fabric for the casing on the line. Cut out the circle and then sew the last casing seam around the edge.