The Shadow of Four by Melanie Vandonk:
 
After the death of her mother, “Girl” wants nothing more than to fade into obscurity behind the clandestine walls of the Faith of the Four Spirits Monastery. As an exceedingly rare magic wielder who possesses the ability to manipulate all four elements, Girl is worshipped as a divine being but forced to train the very power responsible for her mother's murder.

Girl is resigned to an isolated existence until a stranger appears on the Monastery doorstep in the middle of the night, revealing that Girl may not be as alone as she was led to believe. Determined to uncover the truth, Girl embarks into a world of concealed identities and elaborate deceptions where she learns the leader of the Monastery may have more sinister plans for her followers than mere education.

Girl must decide if her newly forged friendships are worth facing the destructive truth of what she is training to become, or whether she is destined to succumb to the darkness that feeds her.