Fledgling by Octavia Butler

This is the story of an apparently young, amnesiac girl whose alarmingly unhuman needs and abilities lead her to a startling conclusion: She is in fact a genetically modified, 53-year-old vampire. Forced to discover what she can about her stolen former life, she must at the same time learn who wanted-and still wants-to destroy her and those she cares for and how she can save herself.