Three days later, at 1.42pm on Saturday, she was found dead at the Marriott hotel in Leicester.
Her Twitter account – @Sweepyface – was deleted last week, but her tweets can still be seen via this archive which was being shared on Twitter on Monday morning and is purportedly all the tweets from that account.
So what was in the dossier that Sky News said was being handed over to the Crown Prosecution Service? What did @Sweepyface actually say?
Her first tweet, from December 2010, was about the McCanns and accuses others of "unhelpful and uninspired trolling". Over the next four years she sent 4,625 tweets, very rarely on any other subject.
Leyland's account went mostly dormant in 2011 and 2012 but returned with gusto in 2013, some days posting more than 50 tweets, most beginning with the #McCann hashtag.
A common theme, as seen in this tweet on 3 November 2013, is freedom of speech – the idea that the McCanns are trying to silence critics.
Occasionally, Leyland's tweets contained a kind of poetry.
At times, Leyland painted herself almost as a campaigning journalist, as here on 7 December 2013 when she tried to find evidence that royalties from Kate McCann's book were deposited in the Find Madeleine fund.
As well as delivering strongly worded attacks on the McCanns and their actions, Leyland sometimes stuck up for them. On 20 November 2013 she asked why some people were laughing "like demented hyenas" at the McCanns' plight.
And the next day she said that no one wished Madeleine was dead.
To say she was obsessed with the McCanns would be an understatement. She would tweet about the couple's various court and select committee appearances for more than three hours straight.
She would spend entire mornings or evenings conversing with other sceptics, arguing with McCann supporters, or just spouting her views on the latest angle to the case.
Leyland was busy tweeting on Christmas Eve 2013, when she rebuked the person behind the @IAmMaddieToo for being in bad taste.
Leyland concluded that since the McCanns had won such big defamation cases in the High Court (they won £50,000 in libel damages from The Sunday Times just last week) they had waived their right to complain any more.
On 15 March this year, Leyland alluded to attempts made to reveal her identity and tried to throw people off the scent by saying she didn't live in Leicestershire.
Then on 17 March, she said she didn't live in Peterborough either, before adding:
She even wrote a letter to the prime minister – but privately, so her opponents didn't find her personal details.
On 17 September this year she tweeted what might have amounted to a personal manifesto: to make the McCanns "live in shame".
A week later, on 25 September, she sought to justify her hatred of the McCanns:
Before her encounter with Brunt, Leyland was a keen Sky News viewer. On 29 September, five days before she died, Leyland tweeted that Brunt had started following her on Twitter.
Leyland was different in many ways from others who have come to public attention through sending offensive or malicious tweets.
Most observers would agree she was offensive, angry, and bent on causing harm. And there are far worse tweets than the ones listed here – you them read them at this link.
But Leyland's language was polite and measured. She rarely swore (out of more than 4,500 tweets, only 16 contained the word "fuck").
There were none of the physical threats and sexual violence that have typified other high profile "Twitter troll" cases, such as the campaign of abuse targeted at Stella Creasy MP and feminist campaigner Caroline Criado-Perez (which led to the jailing of Peter Nunn last week).
Between bursts of anger and invective aimed straight at the McCann family and what she saw as a cadre of blinkered supporters, Leyland occasionally showed a sense of fairness, and was often keen to stress that a child had gone missing.
Leyland saw her tweets as a public service – she clearly believed that an injustice was taking place. "I'm committed to (finding) the truth of Maddie's death," she said on 15 August this year.
The tweets also give the impression that tweeting about the case was her hobby and that she enjoyed it.
There was a social side to it too. The same names keep cropping up in her timeline, and although she mentioned blocking several "vicious pro supporters", she engaged in some robust Twitter debate, such as the time she called an opponent "an old biddy with huge teeth who tells lies on social media".
She did not fit the usual profile of a malicious speech offender.
Whereas most people convicted of "trolling" offences so far in the UK have been young and misguided, some with drug or alcohol problems, Leyland was a 63-year-old divorcee with two children who had attended Goldsmiths University and a Catholic convent school, the Daily Mail reported.
Her sudden death – plus the footage of her being challenged by Sky News, which has spread like wildfire online – caused an outpouring of sympathy on Twitter this morning, with many blaming Sky News for its perceived role in her death.
A question remains of how the McCanns (who say they don't use social media) were alerted to Leyland's tweets. In a Twitter Q&A on 2 October, the day he visited Leyland's home, Brunt said:
There is a petition at change.org calling on the prime minister to launch an inquiry in Leyland's death, and a Facebook group called Sack Martin Brunt has more than 1,100 likes.
We were saddened to hear of the death of Brenda Leyland. It would be inappropriate to speculate or comment further at this time.
Several people have today pointed to this tweet of Leyland's from 11 November 2013.
Her son, Ben, posted this on Facebook yesterday.
You can call the Samaritans 24 hours a day on 08457 90 90 90, or click here to find out more about its services.
Sky News did not reveal the name or location of Brenda Leyland in its initial report. An earlier version of this post said it did name Leyland