Mrs. Douglas is a 5th-grade teacher at Derry School and is Ben Hanscom, Bill Denbrough, Beverly Marsh, Henry Bowers and Patrick Hockstetter’s teacher. Like most of the adult residents of Derry, she is somewhat aware of Derry's past and that there is something wrong with the town but refuses to talk about it and also has forgotten about It, therefore not believing in it.
She is also aware that Patrick Hockstetter is disturbed, if not aware he is a psychopath, and attempts to keeps him away from the female students, though she is relieved he is a quiet nuisance, unlike the rest of the Bowers Gang. Ben also has a mild crush on her which develops after he helps her out one January afternoon.
She appears in the 1990 miniseries, who appears to be a kind, caring woman who doesn’t like Henry Bowers and often criticizes his behaviour, disciplining it at times, at one time giving Henry detention for one hour after school every day of the week, which he's implied to have skipped.
While she does not appear in the 2017 adaptation nor its sequel, an alternate version of her appears in IT: Welcome to Derry. This version of her is completely different to her character in the book and miniseries, with her character in this version being strict, unreasonable and hostile as opposed as to her kind, caring and warm nature in the book and miniseries. It is also implied she is racist like most of the white people in Derry in the 1960s, treating William Hanlon poorly as opposed to the white students and being quick to suspect him of causing trouble on purpose.