Another welcome Renita.  I think a good many on here are returnees to sewing.  Although I never stopped completely I was amazed at how much had changed (fabrics, tools and techniques) that I didn't know about. I soon found out about them here.

If the fabric hangs ok without the lining I would just go for the slip. 

Yes, it is rectangles joined into strips and the strips sewn together.  No seams to match  as the blocks are set like brickwork.

Are those fabrics in your picture the actual ones you have got for the job?

As it is not a fitted or shaped skirt could you get away with just taking out the excess on the side seam without the zip.  So long as the end result is symmetrical, which you could achieve by folding in half vertically and following the same line for the seam as the side with the zip, it should look ok.

I wouldn't be the least bit surprised if the original turns up now.  The best way to find something you have lost is to replace it.

Hmmm @Renegade Sewist  I think I might need a whip and mask to complete that ensemble. 
 I was hospitalised many years ago when a mosquito bite caused an infection which caused an abcess in a lymph gland.  I had to have surgery and still bear the 3" scar in my groin.

I love that Acorn.  I fancy doing a couple for our caravan.  I'd never come across quillows before you started on yours.