Lucy Cartwright

Lucy Cartwright was a little girl who was walking home from a party with a red balloon when, on 10 November 1913, one of the animated scarecrows from Mr Clark's field kidnapped her and took her to the Family of Blood's invisible spaceship. Daughter of Mine took over her body, killing her. (TV: Human Nature)

It was believed by Joan Redfern that Lucy's parents realised Daughter of Mine was not her and were swiftly killed. (TV: The Family of Blood)

Behind the scenes
According to Doctor Who: The Encyclopedia, Lucy Cartwright was six years old, and also confirmed Redfern's beliefs about her parents' deaths as true; after being possessed, she went home and killed Mr and Mrs Cartwright.