Princess For Hire by Lindsey Leavitt

Desi Bascomb's life changes drastically when she suddenly meets a woman, who is rising up from a bubble in her bath. Earlier Desi read an advert where the Princess Agency called for stand-in princesses. The well dressed bubble woman steps out of the bubble, and wants to know right now if Desi wants to do the job. For Desi, who's been longing for some glamour in her Idaho life, the choice is a definite yes.
Desi has a rare ability: with the help of "Royal Rouge," she can temporarily transform into the exact look-alike of any princess who needs her subbing services. Dream come true, right?

Well, Desi soon discovers that subbing involves a lot more than wearing a tiara and waving at cameras.... In this winning debut, one girl's dream of glamour transforms into the desire to make a positive impact. And an impact Desi makes, one royal fiasco at a time.
 
I loved Princess For Hire! I actually read the Dutch edition of it, but it was just as great ofcourse!
It was a very fast paced read and well written.Just read that there will be a sequel out later, called The Royal Treatment, and it will be out in May 2011, and I am already looking forward to read it! Fans of the Princess Diaries, take a look at this book!