"I don't know if she should worry too much, I mean some of our greatest writers have had movies made of their books, lots of Hemingway novels were turned into movies, it doesn't hurt the book"

Paul Auster is recommending that the person should not worry too much about having their book turned into a film. He is mentioning that a few of the best writers have had their books developed into films, such as Ernest Hemingway. He is implying that having a book turned into a film does not remove from the original work, and that it can even be useful. He is recommending that the individual ought to not be worried about the movie adjustment of their book, as it will not injure the original work. He is encouraging the person to welcome the chance and to not fret too much about it.