In the novel Death on the Nile, Cornelia Ruth Robson is a young woman who lives at The Red House, Bellfield, Connecticut. She is a cousin of Marie Van Schuyler. Her father Ned was almost forced into bankruptcy, due to Melhuish Ridgeway's economic speculations. She went with her wealthy relative on a boat trip on the Nile, where she occupied cabin forty-three on the port side. On the trip she met, and fell in love with Dr. Carl Bessner, who proposed to her.
Cornelia is described as a "big clumsy looking girl with brown doglike eyes". Miss Van Schuyler takes her on the trip to Europe as a social companion, and says that Cornelia has always been "a nice handy girl, willing to run errands, and not so selfish as some of these young people nowadays". Elsewhere, Cornelia is described as being of "an amiable disposition and disposed to like all her fellow creatures".
Dr Bessner instructs Cornelia in Egyptology, as culled from the pages of Baedeker. He finds it a pleasure to instruct her, because she listens intelligently.
On the evening of the murder, Cornelia goes ashore to visit the temple at Abu Simbel, along with Mr Ferguson. She comments wonderingly on the difference made by viewing the temple in artificial light.
Mr Ferguson asks Cornelia Robson why she allows Miss Van Schuyler to bully her, and tries to convince her that everyone is born free and equal. She says that they are not, and mentions that she would have liked to be born elegant and beautiful like Linnet, but she was not. Mr Ferguson says that Linnet ought to be shot as an example. He also tells Cornelia that she is the nicest person on the boat, which makes her blush with pleasure.
On her return to the boat, Cornelia is ordered by Miss Van Schuyler to look for her velvet stole. Mr Fanthorp assists her, but they are unable to find it.
After Miss Van Schuyler has gone to bed, Cornelia returns to the saloon with her embroidery. Jacqueline de Bellefort joins her, and asks Cornelia to tell her about herself. Cornelia is conscious that what she is saying is uninteresting, but she is flattered by Jacqueline's apparent interest. She also gets the feeling that although Jacqueline is looking at her, she is listening to, or for, something else.
Cornelia is present when Jacqueline shoots Simon Doyle. She runs out of the saloon to get help, and finds Mr Fanthorp. Cornelia and Mr Fanthorp take Jacqueline to her cabin, and Cornelia fetches Miss Bowers to look after Jacqueline.
Cornelia later assists Dr Bessner as he is attending Simon Doyle, and exhibits "superior fortitude".
After the deaths of Louise Bourget and Salome Otterbourne, Cornelia says that the trip has been like living in a nightmare, with three deaths occurring. Mr Ferguson tells her that it is the future that matters, not the past, and that no one really cares whether Linnet, Louise, and Mrs Otterbourne are dead or not. Cornelia tells him that he is wrong, because Rosalie Otterbourne was fond of her mother, and someone somewhere must have been fond of Louise. She also says that Linnet was beautiful, and when anything beautiful is dead, it is a loss to the world.
Mr Ferguson tells Poirot that Cornelia's father was practically ruined by Linnet's father, Melhuish Ridgeway, but Cornelia did not bear a grudge against her. Cornelia admits that she did feel sore towards Linnet for a minute, because her father died of discouragement.
Mr Ferguson asks Cornelia to marry him. Cornelia turns him down, saying that he is not serious, because he laughs at serious things like education, culture, and death, and so he would not be reliable.
Cornelia is present at the denouement, along with Dr Bessner. She finds out about Miss Van Schuyler being a kleptomaniac, and mentions how worried she has been because of the shame that the family would face if it became publicly known. Dr Bessner says she is so worried because she has a heart that is too tender, and she has a "very sensitive and beautiful nature".
At the end of the novel Cornelia reveals that Dr Bessner has proposed to her, and she has accepted. Mr Ferguson cannot believe that she would rather marry Dr Bessner than him, but Cornelia says that the doctor is kind, and she has always been interested in clinics, and will have a wonderful life with him. She says that Dr Bessner has said that she could really help him in his work, and that he would teach her all about neurosis.
Mr Ferguson says that Cornelia must be mad, and Poirot explains that she is a woman of original mind, and that it is probably the first time Mr Ferguson has ever met one.
The character of Cornelia Robson was omitted from the 1978 film version. Some of her backstory was instead given to the character Miss Bowers who is the nurse of Miss Van Schuyler. It is Bower's family, for example, who was ruined by Linnet's father. The other part of Cornelia's role, that of witnessing the shooting of Simon Doyle by Jacky, is given to Rosalie Otterbourne. The entire pattern of romantic relationships is also adjusted because of the changes. Dr Bessner does not end up being engaged to anyone. Ferguson does however succeed in getting Rosalie Otterbourne to agree to marry him.
In the 2004 David Suchet adaptation, Cornelia Robson is portrayed by Daisy Donovan. This portrayal is quite fairly to that in the original novel, except that since Bowers is not cast, Cornelia takes over the role of returning the pearls stolen by Marie Van Schuyler and explaining that her cousin Marie can't help what she is doing. Cornelia had been sent on the trip to accompany Miss Van Schuyler and keep her out of trouble. Like in the original, she is one of the few present during the denouement in Simon Doyle's cabin, and she ends up marrying Dr Bessner.