If you're talking about the white one - I made one of those myself for a halloween costume one year. They're super easy, and so long as you can get your sister's meausrements, you should be able to make one without a pattern. I don't have a pic, but I'll draw up a quick tute for ya
K, here goes it: I hope this makes sense with the craptastic paint images I made...
First thing, you need to get those measurements. Then you want to lay out your fabric and cut out the following pieces:
The last piece - you need to cut out two of.
For the cups, cut them out to about twice the width of your sister's underbust per breast (as long as she's busty, I'm sure you can alter this to what she may need) Make them (at the longest point) appx the measurement from collarbone to underbust, over fullest area.
The next pieces are the waist panels. Cut out 2 pieces that are 1/2 her widest midsection measurement + seam allowance. Cut one of them in half as shown.
The piece on the far right is the neck-band.
For the skirt (last piece) make it like a standard circle skirt, but appx. 1 1/2 times her waist measurement (for pleats and fullness)
Take the bust pieces and gather or pleat along the bottom until they are the desired width. Baste.
Take waist panels and trim inwards slightly at the waist, if necessary. Sew the two smaller pieces to the larger one on either side as shown.
Fold neck-band in half length-wise. Cut in half and turn right way round (Inside out) Finish one end.
Sew bust cups to waist (closer together than they are in the image, since my paint skills are just THAT grand - for coverage)
Sew neckband to ends of bust cups.
Finish all edges as necessary.
Sew sides of skirt together (leaving zipper allowance on one seam)
Add pleats around waist to bring to your sister's measurements.
Now, sew down the pleats part way and iron nice and flat.
Sew the skirt onto the waist band, lining up the zipper location in the back of the skirt to two ends of the top.
Hem skirt, finish any unfinished edges, and install zipper.
Voila! Put it on, zip her up, tie her up, and you have this:
I hope this helps you....I also hope it makes sense