The Thirteenth by G. L. Twynham
Imagine starting at the end and finishing back at the beginning. This is the story of a teenage girl called Valerie Saunders who is about to be thrown through time and space. Being bestowed with abilities beyond her wildest nightmares, she discovers that she not only has to deal with turning eighteen, her first job and an unwanted tattoo, but also magical powers and intense urges to fall in love. She envisaged she would spend her life blending into the scenery, not blowing it up! Val has a calling, but which side is dialling her number?