I cut out the shape of the seat top with an extra 1/2 inch for seam allowances. I stitched red piping 1/2 inch from the cut edge with a zipper foot. I also used the zipper foot when I stitched a 7 inch strip all around the seat shape, right sides together. I had to ease around the rounded corners. On the other side of the strip, I made a 3/8 inch casing and inserted 1/4 inch elastic.
I hope she likes it!