First I cut out two pieces shaped like this, that came to a point in the middle, and were wide enough to fit around her waist. I ended up cutting some off in the end, but that's easy to do later.
On one piece, I laid out 5 pieces of ric rac like so, and then sewed them down, sewing straight down the middle.
Then I took some pre-made piping, and pinned it along each edge, with the piping towards the middle.
I clipped the piping at the bottom there a little bit, to fit better around the little point.
Then, using a zipper foot, I sewed AS CLOSE as I could to the piping. Like, really close.