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

Princess Nell is Nell's fictional alter ego in the Illustrated Primer. She is originally the main character in an interactive story that adapts to its reader's environment and requirements. Technically, the storyline followed by Princess Nell goes as follow: She was found floating at sea along with her brother Harv. She was raised by a fisherman and an evil stepmother.