Mary Poppins is a cherished childhood movie for so many since it's release in 1964, but it turned out to be a nightmare for the original author, P.L. Travers.
Mary Poppins was originally written as eight children's books that were published from 1934 to 1988. The first three books consist of Mary Poppins "popping-in," being a nanny for a family, before promptly "popping-out" and abruptly leaving. The final five books recount other adventures Mary Poppins had during her first three visits.
Walt Disney attempted to buy the rights to Mary Poppins as early as 1938, but Travers refused, knowing a film adaptations would not do her work justice. By 1961, Disney finally prevailed, though Travers got the script approval rights.
In the film, to Travers' displeasure, Mary Poppins was portrayed as much kinder and gentler than in the books. Travers also hated the animated scenes, which she wanted to avoid when she first refused to give Disney the movie rights. She made many changes to the script, most of which were disregarded.
The only reason she was able to go to the movie premiere was by shaming a Disney executive for an invite. When there, she cried the whole time and refused to let Disney touch the rest of the series.