The Protectors: Book 1 in the Protectors Saga

Avery Kimball's happy world is turned upside down when she learns that she and her four best friends were once a group of powerful warriors charged with protecting a distant planet. Sent to Earth to be re-born after being killed by the Emperor, Avery and the others must now return, although settling back into her role as a warrior isn't easy, especially with her attraction to the mysterious King.