Hi @joslyn sorry for the delay in any reply.
Do you mean adding a gathered ruffle of organza to the lining, which will then show below the skirt hem?
Here’s how I would do that:
Calculate depth of ruffle – work out how much you want to see below the dress. Add 1/2 to 3/4 for a narrow or rolled hem.
Then add another 2 inches so that you can attach it to the lining an inch and a half or so above the lining hem, that way the attachment seam won’t show when it’s worn.
Now, to calculate the length: Depends on how gathered you want it, but maybe twice the circumference of the lining skirt bottom.
Then sew two sections of gathering stitches, breaking at the side seams. Gather it and spread the gathers evenly then stitch it down.
You could finish the top edge of the gathered ruffle first with either a serger or a narrow hem.
Hope that help. It’s a very pretty idea.