Cinderella is a well-known classic folk tale embodying a myth-element of unjust oppression/triumphant and reward.
The word "cinderella" has, by analogy, come to mean one whose attributes are unrecognised, or one who unexpectedly achieves recognition or success after a period of obscurity and neglect.
A Cinderella Bride is a woman who is unrecognizable on her wedding day because of her new found beauty. Usually the bride has used her wedding date as motivation to lose weight and dropped many pounds. She splurges on a beautiful dress that she would otherwise never have put on because she prefers to wear sweats and t-shirts. She has her hair uncharacteristically styled at a chic salon and her make-up done by an artist.
Like Cinderella, when the ball is over, she goes back to being plain and mundane. But, she does have some nice pictures.
"Andrea was a Cinderella Bride. She dropped like 50 lbs, put on some make-up for the first time and looked great in her wedding dress."