Magic or Madness

Reason Cansino is a girl who is great with numbers. She also has a grandmother she hates, and a mother who's gone crazy. She and her mother have been fleeing her grandmother, while living all over Australia. Then, she finds out that magic is real, and if you don't use it, you turn crazy. But, if you do use it, it sucks up the time you have to live. If you want to find out what happens, read Magic or Madness, by Justine Larbalestier.