Alan is totally correct in his making a skirt for a girl shape. It's called slope.

I do this to every kilt I make. If the customer wears his kilt at full rise the slope is minimal.
But the lower the kilt is worn the more important slope becomes.

This is true for people who have lots of shape too.

A lot of kiltmakers look at me weird when I tell them I put slope in a kilt. They have never heard of it before. But if you look at the kilts in the photo that goes around the forum from "The Windsor Style" of the kilts hanging in the closet you will see slope in them.

If my explanation of slope is still not making sense simply put on a pair of jeans and stand sideways in front of a mirror. You will see that the waistband is significantly higher in the back than in the front. This is slope.