Who is Rosalie Otterbourne from Death on the Nile and what is their importance?

Rosalie is the daughter of novelist, Salome Otterbourne. She is described as moody and unfriendly. Rosalie becomes a suspect in the murders because she is seen throwing something off the ship, which is believed to be the murder weapon. Though she did, in fact, throw something overboard, it was not a weapon but rather her mother's alcohol bottles. Salome was an alcoholic.