Ella Dethroned (Song of the Worlds Book 0) by Brandon Barr

Hunted and desperate, Ella, the former ruler of her Realm, must evade the king's assassins and fulfill a mission given her by the gods. Ella carries an otherworldly device, the purpose of which she does not know, but if she is to grasp hold of a prophecy spoken over her, she must survive to deliver the item to a mysterious man named Quanthum. Her only aid is her sharp intelligence and a devoted soldier named Rathan, who has sworn to protect her.