I'm going to assume that you're talking about the Pokemon Bellosom, right?
Here's a Reference so it'll be easier.
Okay, this can easily be solved with a wired hoop skirt from the Renissance time and just cut out, I'm going to say either, silk or cotton fabric for the patterns of the skirt. The top part can easily be a leotard, which that calls for stretch fabric.
So, yeah just find something simple and cheap for the skirt and try to find a wired hoop skirt so that can be a base for the skirt aspect.
I hope this helps and good luck