The Salt Path, and its recent film adaptation, told the story of a couple who decide to walk the 630-mile South West Coast Path after their home is repossessed.
The Observer alleged Winn had misrepresented the events that led to the couple losing their home.
Rather than losing money in a bad business deal, as the book described, the newspaper said the couple had lost their home after Winn had defrauded her employer of £64,000.
According to the Observer, the couple borrowed £100,000 to pay back the money Winn had been accused of stealing, and it was when this loan was called in that their home was repossessed.
It also said it had spoken to medical experts who were sceptical about her husband Moth having corticobasal degeneration (CBD) as she described in the book, given his long survival after diagnosis, lack of acute symptoms and his apparent ability to reverse them.
In a statement issued to BBC News, the publisher said: “Penguin (Michael Joseph) published the Salt Path in 2018 and, like many readers, we were moved and inspired by Raynor’s story and its message of hope.
“Penguin undertook all the necessary pre-publication due diligence, including a contract with an author warranty about factual accuracy, and a legal read, as is standard with most works of non-fiction.”
A legal read means the book would have been looked over by a lawyer before its publication.
“Prior to the Observer enquiry, we had not received any concerns about the book’s content,” the publisher added.
In her statement released earlier this week, Winn said: “[Sunday’s] Observer article is highly misleading.
“We are taking legal advice and won’t be making any further comment at this time.”
The statement continued: “The Salt Path lays bare the physical and spiritual journey Moth and I shared, an experience that transformed us completely and altered the course of our lives.
“This is the true story of our journey.”
The Salt Path has sold more than two million copies since its publication in March 2018, and a film adaptation starring Gillian Anderson and Jason Isaacs was released earlier this year.