Ping's birth and role as a Dragonkeeper was actually foretold by a prophecy: In the second year of Emperor Wu, a new Dragonkeeper will appear. She will be shunned, but she is the true Dragonkeeper.
She was Given as a servant to Master Lan, by her parents because they couldn't find enough money and food to keep her. She is the true Dragonkeeper, and had taken care of Long Danzi and Long Kai Duan.
In the beginning of the book, Ping is a slave girl at the Huangling palace far to the west of the Han empire. She doesn't know her name, her age, or who her parent's are. She only knows the bitterness and hunger of being a slave. She works for the lazy and cruel Master Lan, who treats her as bad as the animals that she cares for. While she feels comfortable around most of the animals, there are two dragons down in a pit that she is wary of. While down there one day, she takes the food of the dragons for herself and her rat Hua. This results in the death of one of the dragons and the dragon's body is pickled so it can be eaten. Through a strange turn of events, involving Ping treating the remaining dragon better, the emperor visiting, as well as being able to hold responsibility for something(the dragon stone).
And them's the facts.