Catherine Asaro - [The Lost Continent 01] The Charmed Sphere

Chime is living an idyllic life with her family in the rural hamlet of Jacob's Vale. But her life is turned upside down when one of the King of Aronsdale's most trusted advisers, searching the kingdom for shape-mages, identifies her as a promising mage with powerful undeveloped ability. Chime reluctantly agrees to travel to Castle Suncroft, where she is to be trained in the art of magecraft -- and also groomed for her marriage to Prince Muller, the heir to the throne of Aronsdale!

Muller is the nephew to the king, and the last thing he wants to do is get married and rule a kingdom. He's more concerned with fashion than affairs of state. When the King of Aronsdale dies and Muller continues to postpone his royal ascension, the leader of a neighboring kingdom -- along with an insane mage bent on destroying Aronsdale -- sees the transition as the perfect time to strike.