Look at going down a size as the material has Elastane or Lycra blended in so it will stretch. There is also the possibility of wearing hip and butt pads…
I have this problem, but in reverse: waist 34” and hips 44”-45”. A size 14 is 33” waist with a 41.5” hip. That’s what I wear and it stretches and/or remolds enough so it works.
I don’t think petit sizing will work as it is usually just a length change to fit a shorter person.
However, junior sizing might work. These are designed to fit a smaller (thinner) person. You’ll have to find a different brand as I don’t think Gloria Vanderbilt offers that size range.
For dresses, there is a style called Fit & Flair. Above the waist is designed to fit and below the waist is very full. It is a way of disguising the hips and works for large and small since it isn’t fitted to the body…