Who is Lucrezia Borgia from Mirror Mirror and what is their importance?

Lucrezia Borgia is the daughter of Rodrigo Borgia, who later becomes Pope Alexander VI. Her mother is the courtesan, Vannozza Cattanei. Lucrezia and her brother, Cesare, have an incestuous relationship that produces her son Michelotto (the gooseboy). She is described as beautiful, vain, vindictive, and cruel.