Corset DressesTue 14 February 2017 by Fausto
From the shape, I suspect one, probably more hoops underneath waist-trainer.org/ann-chery-corsets-review, in a separate cage worn underneath everything else, the last hoop looks like it's around the line of dark red trim on the skirt. The white flounced underskirt hides the hoop lines, and I see a hint of one more layer underneath that one. You could also make it with a full petticoat, though it would be a bit more work to get that bell shape (and maintain it).
I've never made one like that before either (but you are seriously tempting me... ), but it should be a similar exercise to making a dress that goes snugly over a corset, or making a new corset but just extending it with a bouffant skirt. You could possibly "pattern-bash" two patterns together, a corset with a bell skirt (maybe part of a vintage 1950's pattern), starting with a paper model to get the general feeling of it, to locate any trouble spots, then maybe a model out of scrap fabric or go directly to making the real deal but with a lot of leeway to work with (test wear, note and perform adjustments, test wear it again, etc.). In any case, starting from scratch involves more thinking ahead before making the first stitch.
Ijust looked a little closer at the photos in question, and I see a hint of a transition between the corset part and the skirt part, just about where the bottom of a corset would be. It looks like there is a slight discontinuity in the fabric pattern at that point, barely visible at that resolution, and a bit of a step down from the corset to the skirt. You may have an easier job of it - it is very likely that the two are separate garments.