The Born Queen by Greg Keyes

War is coming.

With the usurper Robert Dare having fled, Princess Anne has finally ascended to the throne to the Kingdom of Crothney, but it may already be too late to stop the approaching destruction. Dark monstrosities prowl the countryside, and as the holter Asper soon discovers, the Sedos power that granted humanity its freedom may now be responsible for the corruption that will eventually destroy it.

As the combined forces of Hansa and the Holy Church mass against the Queen they claim to be an unnatural shinecrafter, Anne's mother Murielle sets out on an embassy of peace to Hansa, accompanied by the knight Sir Neal MeqVren. But, there is more to Murielle's mission than first appears, a fact that puts both of them at the mercy of Hansa's unstable king, and the unkillable Robert Dare.

The world has been poisoned, and only the one who gains control of the legendary Sedos Throne can heal it. Anne knows that it must be her, but as she embraces her powers, and the violent impulses they bring, she finds herself changing. Only she can stand against the forces that threaten Crothney, but the cost of her victory may be too great for the world to bear...