Diana L Paxson 
Lady of Darkness 
Book Two of the Chronicles of Westria

The kingdom of Westria rejoices. At last King Jehan has found his bride, a Queen to be Mistress of the Jewels and wield their magical power over the elements. But little does the young and gentle Queen Faris know of the treachery and jealousy that festers in the Westrian court. Being Mistress of the Jewels is a dangerous task, and a resentful sorcerer at court threatens to take away not only her power, but the life of her King. As Jehan lies gravely ill, Queen Faris must battle Westria’s darkest threat since the Cataclysm as chaos descends upon the kingdom.