The Wonder by Emma Donoghue

Lib Wright, a young English nurse, arrives in an impoverished Irish village on a strange mission. Eleven-year-old Anna O'Donnell is said to have eaten nothing for months but appears to be thriving miraculously. Lib's job is simple: to watch the girl and uncover the truth.
An educated sceptic, Lib expects to expose the fast as a hoax right away. But as she gets to know the girl she becomes more and more unsure. Is Anna a fraud, or a 'living wonder'? Or is something more sinister unfolding right before Lib's eyes?
Written with all the propulsive tension that transported readers of Room, The Wonder asks what lengths we would go to for the love of a child.