Miss Thornton is an artist who appears in Where is Susan? When Susan and Midge are entering St. Mark’s, the “beautiful Russian spy” is turned away by the beadle. A tall Englishwoman carrying painting gear explains to the girls that the spy’s entry is barred due to her inappropriate backless dress. Susan decides that this woman is a schoolmistress. On the way out, in an attempt to avoid being detected by the mysterious spy, Susan and Midge separate and Susan latches on to this tall woman and borrows her stool to use as a “hat”. Her suspicion that the woman is a teacher is apparently confirmed when the woman corrects Susan’s grammar. The woman thinks that her new companion’s behaviour is rather odd but takes a liking to her and offers to see her safely to the pier where she has arranged to meet Midge. She is surprised by Susan’s knowledge that the horses at St. Mark’s are Greek and gives her a charcoal sketch that she has made of the statues. Susan is delighted and grateful as they part company. Later, when Charlotte sees the drawing she informs her cousin that her new friend is no school teacher. She recognizes the signature, Thornton, as being that of a very famous artist, a woman far above the class of the Gascoignes’ stepfather, Sam Pilkington. At Selina Gascoigne’s party, Miss Thornton is happy to see Susan again and describes her as a friend, which has Gabrielle seething with jealousy. Miss Thornton is important to Susan because of the drawing (which she cherishes and has framed) and the fact that she provides Susan with one of the few opportunities she has to get the better of Gabrielle.