Daughter/Sister of Mine was a member of a criminal family known only as the Family of Blood in the Doctor Who episodes "Human Nature" and "The Family of Blood". She appeared to be the youngest member, as she possessed the body of Lucy Cartwright (played by Lauren Wilson), a little girl and the youngest of the possessed humans. With her harmless appearance, she was able to infiltrate places, such as the dance hall and the Farringham School for Boys.
When the Tenth Doctor caught her after her family tried to take his life essence, he trapped her inside every mirror in existence. He visited her once a year, every year. Her brother, Son of Mine, wondered if one day the Doctor would forgive her.