In the novel Death on the Nile, Rosalie Otterbourne is the daughter of Salome Otterbourne. She appears sulky and bad-tempered most of the time. Her mother, Salome, is grumpy most of the time, badly bred, grumbling and unpleasant.
Near the beginning of the novel, Rosalie and her mother are staying at the Cataract Hotel in Assuan, along with Poirot. Rosalie tells Poirot that Assuan does not suit her mother, and that she will be glad when they leave on the cruise on the Karnak.
Rosalie and Poirot watch passengers disembarking from one of the Nile steamers, and see Simon and Linnet Doyle come ashore. Rosalie says that it is not fair for one person to have money, good looks, marvellous figure, and love. She says that she would like to tear Linnet's clothes off her back and stamp on her "lovely, arrogant, self-confident face", and that she has never hated anyone so much at first sight.
While on the cruise on the Karnak, Poirot tells Rosalie that her mother wants her. Rosalie had been laughing, but her face clouds over. After she leaves to go to her mother, Mrs Allerton says that she cannot make Rosalie out, as she is friendly one day, and positively rude the next. Tim Allerton says that he thinks she is throughly spoilt and bad-tempered. However, Mrs Allerton says that she thinks Rosalie is unhappy.
After the death of Linnet Doyle, Rosalie is interviewed by Poirot and Colonel Race. She enters ungraciously, and does not look "nervous or frightened in any way--merely unwilling and sulky".
Miss Van Schuyler had told Poirot and Colonel Race that she had seen Rosalie throw something overboard during the night. However, Rosalie says that she did not leave her cabin and did not throw anything overboard.
It is revealed that Mrs Otterbourne drinks, and had a secret supply of spirits which she kept hidden from Rosalie. Poirot explains that he saw that in spite of Rosalie's "carefully studied unfilial remarks", she was actually passionately protecting her mother from something. He suggests that Rosalie had discovered the hiding place of her mother's liquor, and had waited for her mother to be asleep before throwing the bottles overboard. Rosalie admits that this is true, and that she did not say so earlier because she did not want everyone to know about it.
Rosalie tells Poirot that she had tried hard to keep anyone from knowing about her mother's drinking. She says that she had to always be on the watch, and get her mother away from people before any quarrels or rows broke out. She also tells Poirot that her mother has turned against her, and she thinks her mother almost hates her sometimes.
Rosalie says that people think she is awful, stuck-up, cross and bad-tempered, but she cannot help it, as she has forgotten how to be nice. Poirot says that she has carried her burden by herself for too long.
Poirot asks Rosalie if she saw anyone on the deck when she went to throw the bottles overboard, and she says she saw nobody.
The passengers and their cabins are searched, and a small pearl-handled pistol is found in Rosalie's handbag.
Poirot later finds Jacqueline de Bellefort and Rosalie together, comparing lipsticks. Rosalie smiles at him for the first time, a "shy welcoming smile--a little uncertain in its lines, as of one who does a new and unfamiliar thing".
After the death of her mother, Poirot tells Mrs Allerton to look after Rosalie, who becomes terribly upset. Mrs Allerton describes Rosalie as "proud, reserved, stubborn, and terribly warm-hearted underneath", and says that Rosalie is inclined to cling to her "in the most pathetic fashion".
Towards the end of the novel, Poirot lays out a case against Tim Allerton, while Rosalie is present. He suggests that Tim could have substituted an imitation string of pearls for the real one before the night of the murder, and Linnet could have realised it. He might then have killed her, as well as Louise Bourget and Salome Otterbourne, to prevent his crime from being exposed. Although Rosalie maintains that she saw no one on the deck, Poirot believes that it was Tim she saw coming out of Linnet's cabin.
However, Rosalie realises that Poirot knows that this is not true, and is saying it for some reason of his own. Poirot explains that he only said this because he wanted Tim to realise that there was a good case against him.
Tim later asks Rosalie why she would not say that she saw him, and she says that she thought they might suspect him. She did not suspect him, as she did not believe that he could kill anyone.
Tim and Rosalie go to tell Mrs Allerton that they are beginning a romantic relationship, and Rosalie sobs happily on Mrs Allerton's shoulder.
In the 1978 Ustinov film adaptation, Rosalie Otterbourne is portrayedy by Olivia Hussey. In this adaptation her role is considerably enlarged. As Cornelia Robson is not cast, Rosalie takes over the role of witnessing the shooting of Simon Doyle and helping Jacky to her room. In this adaptation, she is also made up as a potential suspect because she had a plausible motive. Linnet Doyle was in the process of sueing Rosalie's mother for libel. During an excursion at Karnak, she asked Jim Ferguson if it was true that one could not "libel the dead". This conversation was overhead by Poirot. As the sideplot of the stolen pearls is considerably simplified, and in any case Tim Allerton is not cast, this part of Rosalie's role from the original novel is not depicted at all. Without Tim Allerton and Cornelia Robson in the adaptation, Rosalie becomes Jim Ferguson's love interest (he does not experience any competition from Dr Bessner here), and they end up being engaged at the end of the show. Personality-wise, this portrayal is more like that of Cornelia Robson in the original novel. She is a loyal daughter in spite of her mother's shortcomings. The original Rosalie was jaded and cynical.
Agatha Christie's Poirot
In the 2004 David Suchet adaptation, Rosalie Otterbourne is portrayed by Zoe Telford and her protrayal is close to that in the original novel. The only difference is that here she does not end up with Tim Allerton. She expresses an interest in him but he turns her down, telling her that she is "barking up the wrong tree."