P.L. Travers
From what I read in the IMDb trivia and elsewhere on the net for this movie, she sounded like a cranky and chronically unsatisfied woman who can never be pleased. She hated the Walt Disney version of her book, hated the songs and always gave strict consultations on how her works should be adapted to the movie screen and musical theatre versions.
It also took Disney several years to get her agreement for the film. She sounded very stubborn and was obviously very difficult to deal with. She should've been proud and satisfied with the Disney adaptation considering it won 5 Oscars and was a major success, but no, it didn't meet up to her standards for some negative reason.
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Come to Middle-Earth, a world beyond the furthest reaches of your imagination