Reflecting on the legacy of Helen and Edgar, Crain said that while Edgar, who studied journalism at the University of Missouri, produced highly compelling reading, Helen, whose suffragette mother taught her to interview relatives and gave her the camera to take to China, cared more about documenting and recording every single piece of truth for future generations.

"Helen often said to me: 'I don't care if it's published now. Some day it will be'," Crain said. It is believed that when Edgar was writing up his interview with Mao, it was Helen who persuaded him to add more details that eventually turned it into a whole chapter.

In Edgar's 1958 autobiography Journey to the Beginning: A Memoir, he wrote: "I should at least give some account of my life with the very unusual woman who was to be my frequently tormenting, often stimulating, and always energetically creative and faithful co-worker, consort and critic."

Helen said in 1991, when she was 84: "I call my life 'bridging'. All my writing and thinking provides a 'bridge to the future', as I call it. It is a body of writing that bridges over, not between extremes of any kind, to find the valid thesis for building the best future."

Of all her more than 60 books, only seven were published in the US, including the 1984 autobiography My China Years: A Memoir. Loads of unpublished manuscripts and thousands of pictures and letters are now at Brigham Young University in Provo, Utah, as well as the Hoover Institution Library & Archives at Stanford University in California.

The"12 miles of 16-millimeter color film" that Considine had shot of Helen in China in 1978 were still in his keeping. There had been several ill-fated attempts to edit the film into a documentary or TV series, said the director, who still wants to see through "what Helen and I wanted to do first".

Some family members became involved along the way, including Helen's niece Sheril Foster Bischoff, who remembers gazing at Helen's picture as a little girl, enchanted by her effortless glamour.

One year before Helen died, Bischoff and her husband spent five weekend days, 13 hours a day, going through all the materials at her aunt's house in Madison, eventually condensing the 600 boxes to 200.

"We visited Helen for the last time in 1996, to deliver to her the handwritten letter given to us by Huang Hua during our trip to China in June that year," she said. Calling her "Dear Peg", Huang, who died in 2010, wrote: "Now 60 years later, looking back to that dangerous and challenging moment of history, I felt that we lived up to the expectations of our peoples."

These days, An, who has translated four of Helen's works, acted as a de facto consultant for both Bischoff and Adam Foster, Helen's grandnephew who helped set up the Helen Foster Snow Foundation last year and is now its president.

"In her final years, Helen lived a very frugal life-shopping for food about to exceed its shelf life and eating two meals a day," said An, who visited Helen for the last time in August 1995.

"A lot of friends from China offered financial help but she never accepted it, fearing that doing so might jeopardize her reputation as a journalist. She wanted every word she ever typed to carry the weight of a passionate yet objective observer. She's a patriot who loved her country fervently, as she did China.

"She was extremely thin and weak. I asked her to rest, but she insisted that I turn on the recorder. When she was young, Helen dreamed of writing a great American story. All she did was to turn herself into one."