They originally wanted Mary Poppins to be Truly Scrumptious.
In the film, the character of Truly Scrumptious was played by Sally Ann Howes, whose previous credits include Dead of Night, Anna Karenina, Fools Rush In, and The Golden Year. Originally wanted for the role was Julie Andrews, who had wowed audiences with her roles in Mary Poppins and The Sound of Music, but she turned it down feeling that Truly would be far too similar to those other roles. It's the same reason that she would turn down Disney's Bedknobs and Broomsticks too. Interesting bit of trivia: Julie had starred on Broadway in My Fair Lady, and her replacement after she left was Sally Ann Howes. Bet you didn't know that before you checked this out.