The Key of Amatahns — Elisabeth Wheatley

Janir had the misfortune of being born with one of the hated Argetallams for a father. But unlike other Argetallam children, she was mostly granted a normal childhood, away from the rest of her family. It looked as if she would live a relatively normal life as the foster-daughter of a powerful lord. Until one critical day Janir's powers awakened and she became entangled in a young enchanter's quest for a long-lost treasure called the Key of Amatahns...