The Beasts We Bury - D. L. Taylor

Mancella, heir to the throne, emerged from the mysterious Broken Citadel with a strange and violent magic: she can summon an army of animals, but only by killing them first. Silver is a charming thief who plans to manipulate Mancella in order to pull off a once-in-a-lifetime heist. When her father decides that Mance should kill a human in order to create an unbeatable spirit army, Mance realizes how much of a pawn she is in his world. As the deception and bloodshed continue to mount, Mance and Silver find themselves forced to make choices that will change the realm forever.