She'll have to experiement- but any wrap or fitted pattern should work fine as long as it fits well.
Start with your two layers of choice. Attach the fasteners to the front of the outer layer. On the back of both layers do a small casing for elastic. Stitch the elastic. Now put them right sides together and sew from one end of the elastic to the other, doing what ever you need to do for the leg elastic (maybe do a casing, gusset, or sew it to the seam allowance). turn and then finish the fasteners on the tabs.