Yellow Brick War (Dorothy Must Die Series #3) by Danielle Paige

In this action-packed third book in the New York Times bestselling Dorothy Must Die series, new girl from Kansas Amy Gumm is caught between her home - and Oz. My name is Amy Gumm. Tornadoes must have a thing about girls from Kansas, because - just like Dorothy - I got swept away on one too. I landed in Oz, where Good is Wicked, Wicked is Good, and the Wicked Witches clued me in to my true calling- Assassin. The only way to stop Dorothy from destroying Oz - and Kansas - is to kill her. But I failed. Others died for my mistakes. Because of me, the portal between the worlds has been opened. And if I don't find a way to close it? Dorothy will make sure I never go home again. Now it's up to me to- join the Witches, fight for Oz, save Kansas, and stop Dorothy once and for all. Perfect for fans of Marissa Meyer's Lunar Chronicles and Gregory Maguire's Wicked, Danielle Paige delivers a dark, high-octane reimagining of L. Frank Baum's The Wonderful Wizard of Oz.