Claudia Auditore da Firenze
Claudia Auditore da Firenze is the little sister of Ezio. She has been too spoiled by Giovanni: she is smart and kind, but she is immature. She is portrayed by Devery Jacobs in both Assassin's Creed II and Assassin's Creed: Lineage. She appears to be close to her brother Ezio.
Biography
Assassin's Creed: Lineage
Claudia Auditore is a florentine young girl of a noble family living during the 15th century in Italy: the Renaissance. She is the daughter of Giovanni Auditore, an Assassin, a "profession" of her father that she doesn't know.
Assassin's Creed II
After the tragic events that befell the Auditore family, Ezio vows to protect her, along with their mother, and escorts them both to the safety of the Villa Auditore. There, Mario puts her to work keeping a book of finances for the Villa; a task she finds positively scandalous, since it involves 'work'. Claudia remains at the same desk for 20 years over the course of Assassin's Creed II. The only interaction that player can have with her, is to read "the book" which shows financial information about the Villa and Monteggiori.
Note Claudia is one of the few noticable people that apparently don't age in Assassins Creed 2; along with Leonardo Da Vinci despite the game taking place over about 23 years.