A book idea - what do you think of it?

It sounds like something that would appeal to young adult readers. However, pay attention to the character arc. Your description is only half of that. You last sentence implies the other half. I hope you've given some thought to how Sarah will grow as a consequence of her tumultuous journey. If you don't know what I mean by the character arc (or arch), look here: a href="http://en.wikipedia.org/wiki/Character_arc" rel="nofollow"http://en.wikipedia.org/wiki/Character_a…/a or do a Google search on the term.