If you added a flannel panel down the center, size of the actual bed, it would not have to go to the edges either on the sides or at the bottom. Could be serged or turned under and hem stitched down. Then hand stitched, basted, snaps, velcro tabs, ties could hold it in place. The front wouldn't be affected at all, and the back panel could be removed for washing. No long arm needed, and you could roll up the edges and center on your table to make it work. Cheap and easy...if she sews she could do it!