The Bride to be will, ofcourse, be sandy:

 Sandy Costume

And the rest of the girls get to be her Pink Ladies:

 Pink Ladies Costume

Remember that its the job of the brides maid to make the hen’s night as memorable as possible. Don’t forget to keep track of how many chat up lines get used that are taken directly from the film. Maybe even reward the guys with lollipops or a cheeky kiss.