Emma is described as a "middle-aged woman with no very outstanding characteristics, neither good-looking nor plain". She has dark hair, which she wears swept back from her forehead, steady hazel eyes, and a very pleasant voice. She is five feet and seven inches tall.
Dr Quimper says that Emma has the instinct some women have to make their menfolk happy. She sees that her father likes being an invalid, so she lets him be an invalid, although there is nothing really wrong with him. She also let Cedric feel that he is a good painter, let Harold know how much she relied on his sound judgment, and let Alfred shock her with stories of his clever deals. Dr Quimper feels that she would have been a good wife and mother.
When a woman's body is discovered in the Long Barn at Rutherford Hall, and it is revealed that she is probably a foreigner, Emma wonders whether the woman could be Martine, a French woman her brother Edmund Crackenthorpe had been in love with. Emma had received a letter from Martine, saying she and Edmund had married before he was killed, and that they had a son. Emma had arranged for Martine to come and meet the family, but had then received a message from Martine saying she had to return to France and could not see them. Emma wondered whether she should tell the police about this. Her brothers all felt that it was unnecessary, but Dr Quimper encouraged her to tell the police, as she would go on worrying otherwise.
Emma tells Inspector Craddock about the letter. She also says that she was very fond of Edmund, and that he was her favourite brother. She was not sure whether the letter from Martine was genuine or not, but she had wanted it to be true, as she would have been glad if Edmund had left a son.
When the police question Cedric about his movements on the day of the murder, Emma tells him that it is serious, and urges him to tell Inspector Craddock exactly what he was doing on that day. Inspector Craddock does not question her about her movements, because the murderer is known to be a tall dark man. However, Emma provides an account of her movements anyway. She says that she went into Brackhampton for a meeting of the Church Restoration Fund, and has lunch with Lady Adington and Miss Bartlett at the Cadena Café. She then went shopping, and went to the station to meet Bryan Eastley, who was arriving by train.
Inspector Craddock shows Emma an envelope which was found on the grounds of Rutherford Hall. It is addressed to Mrs Martine Crackenthorpe. Emma recognises it as the letter she had written to Martine. This seems to suggest that Martine did come to Rutherford Hall, and that the dead woman may have been her.
Later in the novel, Emma is taken ill, along with the rest of the Crackenthorpe family. According to Lucy Eyelesbarrow, Emma was quite seriously ill. Dr Quimper told Lucy to look after Emma especially, because she means a lot to him.
In MGM's 1961 adaptation Murder, She Said, the part of Emma is played by Muriel Pavlow.
In NHK's anime adaptation 4:50 from Paddington, the character of Emma is voiced by Emi Shimohara.