How can we say that Pamela is the hero of the story?

When the Viscount Medardo is split in two during a battle against the Turks, his good and evil halves take a life of their own. The people of Terralba soon find themselves suffering under the actions of both Medardos. Pamela, a peasant girl, becomes engaged to the evil Medardo. The good Medardo challenges the evil Medardo to a duel for Pamela's hand in marriage and both are wounded in the process. After the duel, both Medardos are reunited into one, becoming a whole person again.
A major theme of this book revolves around the dichotomy of good and evil. The author shows the importance of balance and wholeness through Pamela. Because of her desire for a complete person as a husband, Pamela reunites the split Viscount Medardo and also brings stability back to Terralba as a result.