Great-aunt Mary

In the novel Dumb Witness, Great-aunt Mary is mentioned. She is the great-aunt of Arthur Hastings.

When Poirot receives a letter from Emily Arundell, he shows it to Hastings. Hastings compares Miss Arundell's handwriting to that of his Great-aunt Mary, which he says is like a spider got into an inkpot and is walking over the paper.