Ember — Carol Oates

When Candra Ember wakes up in hospital after a dangerous encounter with a red-haired woman, she is shocked to discover that seeing a winged boy wasn't her imagination. Candra is exposed to a world of rivalry and sacrifice she never knew existed, and the aftermath of a war to save humanity thousands of years ago. Soon she finds herself relentlessly stalked by Sebastian, a beautiful and arrogant Watcher Angel and romantically pursued by his darkly seductive rival, Draven. Ultimately, dubious about her own goodness, Candra's very existence compromises a tentative peace in the city of Acheron.