My Fairly Dangerous Godmother (My Fair Godmother #3) by Janette Rallison

Some people bomb auditions. Sadie Ramirez throws up during her tryouts on TV show America's Top Talent. Her performance is so bad, it earns her a fairy godmother through the Magical Alliance's Pitiful Damsel Outreach Program. Enter Chrysanthemum Everstar: a gum-chewing, cell phone-carrying, high heel wearing fairy godmother in training. She misinterprets Sadie's wishes and sends her back in time to be a part of The Little Mermaid story and then makes her one of the twelve dancing princesses. Wishes are permanent, and if Sadie wants to get back to her home, she'll have to strike a magical bargain--one that involves stealing a goblet from a powerful fairy queen.