Didn't see the show, but they are really easy to make!
Step one- Measure how long you want your dress to be, and cut the pillow case from the seamed end- the hemmed end will be the bottom of the dress.
Step two- Fold the pillowcase in half, and cut a rounded L-shape for the armholes- about 3 by 3 inches is what I use.
Step three- Not sure if this is how it was done on the show, but, this is how I do it, lol. Using the cut-off scrap piece, make a binding for the arm holes by cutting a two inch wide piece by however long your arm hole is, fold in half lengthwise, press, and then fold in the cut edges, press. Use this as you would bias tape, or use purchased bias tape to bind the armholes.
Step four- fold overthe top edgehalf an inch or so and topstitch on both sides. This will be the casing for your ribbon.
I have done this another way also- instead of ribbon in the neckline, I have done elastic to fit, and just extended the bias tape in the armholes to make them long enough to tie at the shoulder. With this method, you don't have to worry about the ribbon coming out in the wash.