Looks like two layers to my eyes. One is long, with the ruffle along the bottom. Second piece tucks into the other, and includes a weird extra piece of fabric in front and back bow.
I would make the bottom layer first, making sure it fits. Then add the top layer and add snaps to attach, tucking it into the bottom skirt. Maybe add two snaps below the navel on either side, and on the sides.
It might also help to sew in some of the tucks. You may also want to add some interfacing along the back of the upper "skirt" to maintain its distinctive, inverted "V" shape, help keep the bow from dragging that layer down.