Homebound (Book 1 of the Starbound Chronicles)

Kaoillana, a young Time Lady from Gallifrey, believes she is the last of her kind. Posing as a human girl, she lives at an orphanage in London, until one day she is kidnapped by a man called Henry Van Statten, who had discovered her alien heritage. Trapped in a secret museum of alien artifacts, she waits in hope of being rescued. One day, a man called the Doctor and his companion Rose come to the museum. From then on she travels the stars aboard the TARDIS with the Doctor and his companions.

DISCLAIMER: I do not own Doctor Who, or any of its characters. I only own Kaoillana.