What is the main conflict in The Lying Game by Sara Shepard?

As the story opens, Sutton Mercer is lying in a bathtub in an unfamiliar room. She can't remember how she came to be there but she also can't remember much of anything about her life. Then a girl enters the bathroom and Sutton tries to make her presence known. The girl completely ignores her and it takes only a little longer for Sutton to realize she's dead. The girl in the bathroom is Emma Paxton. Emma and Sutton are identical twins and were separated, apparently at birth or as very young children. Sutton was adopted by an affluent family while Emma remained with their mother. Sutton has apparently led the life of an indulged child and has turned out to be a selfish teenager. Emma lived with her mother, who showed signs of manic depression, until she was about five, and has been shuffled from one foster home to another.