Who is Dona Luciana from The Viceroy of Ouidah and what is their importance?

Dona Luciana is the wife of Ouidah's first doctor. When she first sees Francisco, she mistakes him for the Devil. When her husband dies of yellow fever, a deathly ill Luciana is taken in by Francisco, and after she recovers, they eventually become lovers. Luciana, who is white, bears Francisco his only white child, Eugenia. Shortly after that, Luciana dies of poisoning by enemies of Francisco.