In the novel The Mirror Crack'd from Side to Side, Margot Bence is a portrait photographer, who took photos at the event at Gossington Hall. In her childhood, she had been adopted by Marina Gregg for about four years, until Gregg became pregnant with her own child.
Margot is described as a "thin girl, all elbows and angles". She has black hair that falls down either side of her face in a "heavy curtain".
Margot had been engaged to take photographs on the day of the fete at Gossington Hall, including photographs of special people being greeted by Marina Gregg and Jason Rudd. She set up her camera on the stairs, as she was able to get a good angle to take photographs of people coming up the stairs below her, and then she was able to swivel around and photograph Marina shaking hands with them.
When Inspector Craddock asks if she had seen any unusual expression on Marina's face, she shows him a photograph which she took of Marina on the day of the fete. It shows Marina staring slightly obliquely to the left of the camera, but with her face expressing nothing. This is the "Lady of Shalott" look that Dolly Bantry had described.
Margot was born in England, and her birth mother had eight children, and lived in a slum. Her mother had written to Marina, asking if she could adopt a child. She thought that she was doing the best for Margot, by allowing Marina to take her, so that she could get the advantages and education her birth family could not give her.
Margot was five years old when Marina adopted her. She had two adopted brothers, Angus, who was older than her, and Rod, who was practically a baby. She lived with Marina for four years, until she was nine years old. When Marina found out that she was going to have a baby of her own, she sent the children to live with a foster-mother, giving them money for their education and a sum of money to start them off in the world. Margot went on to train with Andrew Quilp, at Reingarden Studios.
Margot says that she does not blame Marina for wanting a child of her own. However, she hates Marina for taking her away from her birth family, letting her believe that she was loved and wanted, and then showing that it was all a sham once she found out that she could have a baby of her own.
Margot and her adopted brothers had drifted apart later in life. She says that Rod is a farmer in the Middle West, and that she had lost sight of Angus. The last time she had seen him, he had said he was going on the stage, but she did not know whether he did.
Margot had wanted to see what Marina looked like, and so she did some lobbying to get the job at Gossington Hall. Marina did not recognise her, and Margot did not tell her who she was.
In the EMI films 1980 adaptation, the character of Margot Bence is played by Marella Oppenheim. She has a much reduced role here. The connection about her being an adopted child of Marina Gregg is not part of the plot. She is not interviewed by the police or Miss Marple. Her only appearance is when taking photographs at the fete. It is not even clear that she captured a photo of Marina with the "Lady of Shalott" look. Cherry Baker described the frozen look to Miss Marple and she likened it to the Lady of Shalott.
In the 1992 BBC adaptation, the character of Margot Bence is played by Amanda Elwes. Like in the original story, she was adopted by Marina Gregg. She hated Marina for abandoning her after she had her own baby. She turned up at Gossington Hall uninvited to take photographs of Marina in order to expose her as a vicious and cruel woman. She told Miss Marple that at the end of it, what she got was photograph of a frightened woman. Miss Marple thought it was more a woman who had just received a shock. Before the fete, Miss Marple first saw Margot when she was praying at the village church. From the way she genuflected, Miss Marple observed that she was a Roman Catholic, although the plot significance of this observation is not explained.
In ITV's 2010 adaptation of the novel, the part of Margot Bence is played by Charlotte Riley. The portrayal is faithful to the original.