I was watching the scene from season 1 where Locke sits on the beach beside Shannon and tells her the story of how Boone died. She was crying and seemed relieve to hear the story. The very next scene is Shannon and Sayid in the caves. She says John Locke killed my brother, I want you to do something about that. She almost seemed like a completely different person (nemesis), not to mention she went from the beach to the caves in no time.