She said she felt she wanted to "climb into a hole" and not come out after finding out her diary, which she believed had been taken for a time by the Portuguese police, had been published in the News of the World in 2008.
"I'd written these words at the most difficult time of my life.... It was my only way of communicating with Madeleine," she said.
Mrs McCann and her husband Gerry were giving evidence yesterday to the Leveson Inquiry into media practices.
They said they were left distraught by press suggestions that they were responsible for Madeleine's death, after she went missing, aged three, on holiday in Portugal in May 2007.
"We feel that a system has to be put in place to protect ordinary people from the damage that the media can cause by behaviour which falls far below what I would call acceptable," said Mr McCann.
Mr McCann acknowledged that the media had been helpful when launching appeals - and thanked people who had come forward as a result of them.
But Mrs McCann said she felt the relentless coverage was "stopping their chances" of finding Madeleine.
"She was on the front page every day for a period.... When a story is so negative, it's not helpful," she said.
Mr McCann said the couple also quickly realised there was a "tremendous amount of speculation" and he believed "elements" of the police inquiry were being leaked to the Portuguese press, which was running stories based on "snippets of information".
These were picked up by the British press, which could not tell if these stories were true or not, he said.
"They didn't know the source, they didn't know whether it was accurate, it was exaggerated and often downright untruthful and often, I believe, on occasions, made up," he said.
The inquiry also heard some examples of the articles which led the couple to successfully pursue a libel action, including a Daily Star headline which read: "Maddy 'sold' by hard-up McCanns", which Mr McCann said "was nothing short of disgusting".
Mrs McCann said the same paper accused the family of storing her body in a freezer.