Publishers don't have to do due diligence when it comes to memoirs and life writing.
There have to be fact checkers for non-fiction work in general to ensure accuracy of facts and data, but people telling their life stories are exempt from this because it's about their life, their memories, etc - and it's very difficult to fact check a subjective version of events.
Penguin therefore wouldn't be liable for anything here.
However, if she's sold this story to Penguin as being truth when it's actually largely fiction, this hugely damages its saleability and doesn't look good for Penguin. It being a 'true' story is what makes it compelling and is what has made it fly off the shelves. A brand has been created around her and the book based on it being a true story of survival against the odds, two ordinary people against the machine of capitalism, etc. Once it no longer fits that narrative, it's not going to be worth the paper it's printed on.
If the article turns out to be true - and we do have to remember that there are two sides to every story, some of the people on the opposing side are now dead, the article itself is quite vague and people's names are withheld so they can't be fact checked, and we don't have access to Moth's medical history - I would imagine Penguin would have to halt the publication of any new editions due to it no longer being the genre it claims to be.
I have to say I am a bit sceptical because it's been ten years since the first book was published, and surely if there were this much bullshit in the book, someone would have been paid a handsome sum by the Daily Mail for an exposé ages ago. Why have all these people stayed silent for so long?
I will watch with interest over the coming days to see if this gets picked up by any other news outlets and any more people from their past come out of the woodwork.