Yes, she played Agatha Christie as a child in flashbacks.
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agatha
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Agatha - 2006 was released on:
USA: 10 September 2006 (Los Angeles International Short Film
Festival)
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Yes, Imelda Staunton appeared in the Agatha Christie adaptation "Murder on the Orient Express" in 2017. She played the character Hildegarde Schmidt in the film.
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Agatha and Tillie Episode 1 - 2006 was released on:
USA: 25 February 2006 (El Cajon Video & Film Festival)
USA: 14 September 2006 (Temecula Valley International Film
Festival)