First, I cut the waistband off. The skirt was pleated, so once the pleats were free, there was a lot of fabric to work with.
Next I cut up the both side seams, on either side of each seam, to remove the zipper and other seam bulk.
Now there's 2 long pieces, one for each skirt. I folded one in half as seen below. The first skirt was going to be the smaller one, so I cut a little off the end so it wouldn't be overly fluffy. You can cut from the top too, to shorten the length. The length should be your desired length plus 1.25 inches for the waistband.
I sewed the side seam together (not pictured) and then began ironing for the waistband. I folded it down 1/4 inch and then 1 inch and ironed all the way around.
I sewed all the way around, leaving a space to insert the elastic. I used a safety pin to thread the elastic through, sewed the ends together, and sewing the opening shut.
Ta-da! That's one! Now you can make a matching one for a sister or friend!