How I Live Now, by Meg Rosoff, 2004

Daisy goes to England to stay with her aunt and cousins to escape her evil stepmother, and finds herself on the threshold of both a passionate love affair and an international war. When her cousin's family is wrenched apart by the military commandeering their homestead, she's forced into a heroism she didn't know she had, and takes a hard second look at her anorexia in a world without food. An extraordinary voice and perspective; Daisy's love affair may disturb some American readers who interpret relationship rules differently than Europeans tend to. Sex alert. Masterfully written.