Diane Duane 
So You Want to Be a Wizard [EPUB ebook] 

A mysterious library book opens the door to a world of magic and danger in the first book in the beloved Young Wizards series. Bullied by her classmates, Nita Callahan is miserable at school. So when she finds a mysterious book in the library that promises her the chance to become a wizard, she jumps at the opportunity to escape her unhappy reality. But taking the Wizards Oath is no easy thing, and Nita soon finds herself paired with fellow wizard-in-training Kit Rodriguez on a dangerous mission. The only way to become a full wizard is to face the Lone Power, the being that created death and is the mortal enemy of all wizards. As Nita and Kit battle their way through a deadly alternate version of New York controlled by the Lone Power, they must rely on each other and their newfound wizarding skills to survive–and save the world from the Lone Ones grasp.