Who is Eugenia da Silva from The Viceroy of Ouidah and what is their importance?

Eugenia da Silva, also known as Mama Wéwé or the White One, is the only white daughter of Francisco Manoel da Silva. She is about 120 years old when the novel begins and at its ending, when she dies. In between, her life story is told. She is born in 1854 to Francisco and Luciana, the widow of an Ouidah doctor. Eugenia is a sickly child whose parents die when she is very young. She grows into a beautiful young woman, and falls in love with a British soldier who arrives in Ouidah on a merchant ship.