Who is Fiona Hackworth from The Diamond Age, or, Young Lady's Illustrated Primer and what is their importance?

Fiona is John Percival Hackworth's daughter. She is four years old when the novel begins. She receives a copy of the Illustrated Primer, an interactive book authored by her father but commissioned for another child. When her father is dispatched to Vancouver to serve his ten-year sentence with the Drummers, she keeps in contact with him through the book's interactive and global communication features.