Fairest by Marissa Meyer

Mirror, mirror, on the wall.
Who is the Fairest of them all?

Pure evil has a name, hides behind a mask of deceit, and uses her “glamour” to gain power. But who is Queen Levana? Long before she crossed paths with Cinder, Scarlet, and Cress in The Lunar Chronicles, Levana lived a very different story–a story that has never been told . . . until now.