Ozland by Wendy Spinald (Everland #3)
With Everland and Umberland destroyed, Gwen, Pete, and Alyssa and the other survivors have taken refuge in Evergreen Village in the forest, where they plot to assassinate the Bloodred Queen, while trying to avoid her monstrous creations, and Doc works on his cure for the Horologia virus–but with the Queen of England dead, and the King of Germany either dead or hidden away, who can they trust to save their devastated world?