Miep Gies was one of the persons who helped Anne Frank's family and several other people hide in the "secret annex". She also managed to retrieve Anne Frank's diary after the inhabitants of the secret annex had been arrested.
Miep Gies later wrote Anne Frank Remembered: The Story of the Woman Who Helped to Hide the Frank Family in collaboration with Alison Leslie Gold and published it in 1987, 40 years after the first publication of Anne Frank's diary.
Miep Gies originated from Austria, not the Netherlands, but had lived in the Netherlands since the age of nine. She was fluent in Dutch by the time the Frank family moved to Amsterdam. When I read the Dutch translation of Anne Frank Remembered, I could not find any reason or argument in it for writing the book in English instead of Dutch. I could not find anything about this on Alison Leslie Gold's webpage about the book, nor on the website MiepGies.nl (see e.g. New edition of book by Miep Gies and the FAQ). So why was the book written in English? I know that Alison Leslie Gold is American (and probably didn't know Dutch), which then leads to the question why Miep Gies collaborated with her instead of a native speaker of Dutch?