The usual solution for child bearing hips is to create a normal skirt top from the waist down to somewhere around just below the navel, plus a bit more to attach the pleats. It needs to be long enough to take in most of the expansion, if not all of it, using darts, so the pleats are going to hang almost vertically. As women vary a lot in their shape the actual length required will need to be found by experimenting with a piece of tape tied in a loop to represent the seam line. It will not be the same length all around - you need to get the seam horisontal on a multiplicity of different slopes.

If you have a yen for neatness you can put in a liner or if the cloth is thin enough make it double like a shirt yoke to enclose the top of the pleats.

However - your present problem is compounded as women taper at different rates on different parts of their circumference, this is a good excuse for studying that area should you ever need one.

I can only suggest that you use a lot of safety pins and experiment, try on and adjust until you can get the material to conform to the body shape.