In the novel Death in the Clouds, Mère Angélique is the principal of the Institut de Marie in Quebec, where Anne Morisot was brought up. She does not appear in person, but is mentioned. Anne says that Mère Angélique has always been kindness itself to her.
Mère Angélique reads of the death of Madame Giselle in the paper, and realises that she is probably Anne's mother. She sends a telegram to Anne to give her the address of Maître Alexandre Thibault, and remind her of her mother's maiden name.
Later in the novel, Poirot makes a trunk call to Mère Angélique, who confirms what Anne had said about the circumstances of her having been brought up at the Institut de Marie. She also tells Poirot that Anne worked as a manicurist, and then as a lady's maid, and she left Canada in that capacity. Anne had earlier told Poirot that she had been a manicurist, but did not tell him about being a lady's maid.