The Eye of Zoltar by Jasper Fforde

Although she’s an orphan in indentured servitude, sixteen-year-old Jennifer Strange is pretty good at her job of managing the unpredictable crew at Kazam Mystical Arts Management. She already solved the Dragon Problem, avoided mass destruction by Quarkbeast, and helped save magic in the Ununited Kingdoms. Yet even Jennifer may be defeated when the long-absent Mighty Shandar makes an astonishing appearance and commands her to find the Eye of Zoltar—proclaiming that if she fails, he will eliminate the only two dragons left on earth.
　　　　　　　　　　　　　　
How can a teenage non-magician outdo the greatest sorcerer the world has ever known? But failure is unacceptable, so Jennifer must set off for the mysterious Cadir Idris in the deadly Cambrian Empire—a destination with a fatality index of fifty percent. With the odds against them, will Jennifer and her traveling companions ever return to the Kingdom of Snodd?