The Novice by Trudi Canavan

Even if a magician's powers surface of their own accord, he will soon be dead if he does not gain the knowledge of how to control them." Alone among all the novices in the Magicians' Guild, only Sonea comes from lowly beginnings. Yet she has won powerful allies -- including Lord Dannyl, newly promoted to Guild Ambassador. But Dannyl must now depart for the Elyne court, leaving Sonea at the mercy of the lies and malicious rumors her enemies are busy spreading until the High Lord Akkarin steps in. The price of Akkarin's support is dear, however, because Sonea, in turn, must protect his mysteries -- and a secret that could lead a young novice mage deep into the darkness. Meanwhile, Dannyl's first order to resume High Lord Akkarin's long-abandoned research into ancient magical knowledge is setting him on an extraordinary journey fraught with unanticipated peril as he moves ever-closer to a future both wondrous and terrible. An epic trilogy of the magicians of Imardin, who gather each year to purge the city of undesirables. But a young girl penetrates their shield and secures a place in the Magicians' Guild.