Magic or Madness (Magic or Madness #1)

Magic or Madness by Justine Larbalestier is the first book in a trilogy of the same name. (Justine is married to Scott Westerfeld, writer of the Uglies series.)

Reason Cansino has lived on the run in the Australian outback for fifteen years. She and her mother, Sarafina, were in hiding from her grandmother, Esmeralda. Sarafina is convinced that Esmeralda is a witch. She has warned Reason never to trust her. But when her mother suffers a mental break, Reason is sent to live with Esmeralda in Sydney.

Reason, while planning her escape from her grandmother's house, finds an old key. When she unlocks the back door with it and steps through, she ends up in New York City. Now she must admit that magic is real. She also must find some warmer clothes, as it is January (summer in Australia, winter in New York).

Larbalestier, Justine. (2005). Magic or Madness. New York: Razor Bill.