It's quoted in that Guardian article (link above), so presumably it came from Shirley herself - though these two paragraphs are not consecutive:

Collins sighs at the memory [of the publication of Alan Lomax's history of blues music, The Land Where the Blues Began]. "Alan sent a copy to me with a fulsome dedication written inside it by hand, but in the book itself I was brushed aside. All it said was, 'Shirley Collins was along for the trip.' It made me hopping mad. I wasn't just 'along for the trip'. I was part of the recording process, I made notes, I drafted contracts, I was involved in every part."

So Collins did the only thing she could: she started writing her own version. Her memoir, America Over the Water, was published in 2004 and it finished with the words: "Shirley Collins was there for the trip? Well that's not how I saw it."

[. . .]

Collins kept in touch sporadically with Lomax, but they only met once again, in Brighton in the early 90s. As ever, she says, there was great affection between them, but they argued about Collins' career. It was only after his death in 2002 that Collins properly forgave him.

The final straw was seeing him, debilitated by a brain haemorrhage and unable to speak, in the documentary film Lomax the Songhunter. "To see Alan at the end of that film, in the swimming pool ..." Collins' eyes glisten at the memory. "The light that came in his eyes really broke my heart. I thought, God, I can't end this on a sour note." In the absence of Lomax to speak to, she did the only thing she could: changed the last line of her book. The 2006 paperback edition now finishes with an Appalachian folk song that begins with the words: "But when you're on some distant shore/Think on your absent friend."