The Winter Charlatan - The Storyteller's Series, #3

She will first save the kingdom. Then she'll steal it. The sole heir to the kingdom is destined to sleep for a hundred years. To hide this liability, the queen left her cursed daughter in the care of a trusted lord, while taking his son as her own. Rowan grew up hating the boy who had her crown and vowed to one day reclaim her place as queen. But when a neighboring king threatens a war they won't survive, Rowan must work with the fraud prince to save Elenvérs.
She pledges herself as his spy in the enemy court and lives in the heart of danger. If she can't save her kingdom before the curse hits, there may be nothing left to wake up to. Book Three in the Storyteller's Series. Each book is set in the same world with a few overlaying character, but is a unique plot.