Knife by RJ Anderson

Once upon a time, a fairy is born, called Knife. She lives in an old oak tree at the bottom of a garden. Only the Gatherers are allowed to leave the tree, every since the fairies were cursed and lost their magic. So when Knife becomes the Hunter and learns to do battle in the outside world, every day is an adventure. But don't read this book if you're expecting fairy dust: the last thing Knife is likely to wield is a magic wand...