Rupert Murdoch has four daughters, but sometimes it seems like there are five. The one who looms largest in his life is not a Murdoch by birth, but a tough social climber from Cheshire who is easily recognisable by her long flame-red hair and is now grappling with the biggest crisis of her career.

Rebekah Brooks has stayed close to the media mogul, once described as the Sun King by the journalist Andrew Neil, for a very long time without getting burned. Other products of the Murdoch stable have their day and are then discarded.

But not even the shocking revelation now sending tremors through News International have driven a wedge between the proprietor and his favourite executive. At least, not yet.

Given the closeness of their working relationship, we can take it for granted that Murdoch approved the message Brooks sent to News International staff yesterday, pleading: "I hope that you all realise it is inconceivable that I knew or, worse, sanctioned these appalling allegations."

Its emotive tone, with its seasoning of words like "appalling" and "sickened", bodes very ill indeed for any News International employee whose fingerprints are found at the scene of that phone-hacking episode when Milly Dowler went missing eight years ago. But the email also had another clear message. Other people pay with their jobs when something like this happens – but not Brooks, even though the perpetrators of this "sickening" act were working for her, albeit indirectly. She is safe, for now, because it would hurt Murdoch so badly to lose her.

But it would hurt Brooks even more to lose her job. Others, like the journalists Andrew Neil or Piers Morgan, can fall out with Murdoch and bounce up somewhere else. But for Brooks, there is no visible life after Murdoch. She might it very hard to readjust if she were torn away from the organisation which has nurtured her through much of her adult life. She and Murdoch talk every day. She is not required to answer to anybody whose name is not Murdoch. When the old man enters a crowded room, Brooks is immediately at his side as his introducer and protector.

She is on a par with Matthew Freud, who is married to Murdoch's daughter Elisabeth, as one of the greatest networkers alive. Her façade is steely, but she is also known to make small acts of genuine kindness for which those on the receiving end stay grateful.

She has become accustomed to the high life from being in Murdoch's orbit. She was in the royal box at Wimbledon last Friday, watching the semi-final between Novak Djokovic and Jo-Wilfried Tsonga. During the Glastonbury Festival, she descended, like the footballer Wayne Rooney and his wife, Coleen, in her personal helicopter and was drinking champagne from a glass while others had to make do with plastic cups.

Other women have thoughtful employers and indulgent fathers, but who else but Murdoch would give his favourite daughter manquée a painting by LS Lowry for a 40th-birthday present? The actor Hugh Grant's secretly recorded conversation with a former News of the World reporter elicited another titbit about her whirlwind life: She goes horse riding with David Cameron.

Though she lives in material opulence, Brooks was not born into this. After a state-school education, she studied at the Sorbonne, in Paris, then, at the age of 20, she turned up at the Warrington offices of a newly launched newspaper called The Post, to work as a newsdesk secretary. The paper folded in a matter of weeks and she talked her way into a similar job in Wapping.

More than 10 years later, at the age of 32 in 2000, she emerged into the public eye as Britain's youngest national newspaper editor and the scourge of paedophiles. In the wake of the murder of eight-year-old Sarah Payne, she threw the resources of the News of the World behind a campaign for "Sarah's Law", which would give people to right to know if a paedophile is living in their vicinity.

The paper "named and shamed" several paedophiles, despite warnings that this could incite vigilante action. "I want to encourage the public to be vigilant, not vigilante," she said in defence of the campaign.

Obviously, she would wish people to believe that she and her newspaper were motivated by a wish to allay parents' anxieties about their children's safety rather than to create a sensation that would drive up sales, an idea that has taken a severe knock now that it has been revealed how little the News of the World cared about the feelings of the Dowler family when 13-year-old Milly went missing.

But at the time, the campaign was popular with the newspaper's readers and did her career no harm. In 2003, she moved up to become the first female editor of The Sun, to be succeeded in her old job by her loyal acolyte, Andy Coulson, who later achieved fame as Cameron's chief spin doctor.

Though Brooks excelled in personal relations on a one-to-on level, she learned early on that making public appearances, which required her to think quickly on her feet, was not her strong suit. Giving evidence to the Commons Select Committee on Culture in March 2003, she casually admitted: "We have paid the police for information in the past."

Those words returned to haunt her years later, as the suspicion spread that Scotland Yard had shown a distinct lack of enthusiasm for investigating the phone-hacking scandal because too many of its officers had taken the News International shilling.

She weathered one notable embarrassment during her time at The Sun, when she was arrested in November 2005 for apparently assaulting her then husband, the on-screen tough guy Ross Kemp, whom she had married in 2002.

She had been out the night before having dinner with the Labour politician David Blunkett, commiserating with him over a story in The Independent on Sunday which had forced him to resign from the cabinet for the second and final time. When she returned home, to Battersea, something went seriously wrong – but we have only unreliable rumours about what exactly it was. Police arrived around 4am, after two 999 calls, to find a sorry-looking Kemp. They arrested Brooks and held her for eight hours. No charges resulted.

The fracas coincided with one of Murdoch's visits to London. He was to be seen in Wapping that morning, demanding to know why his favourite editor was not at her desk. Coulson went to her rescue and when she finally arrived in Wapping, Murdoch treated the whole incident as a joke. The following day's edition of The Sun ran a headline saying "EastEnders hardman beaten by lover" – but that referred to the actor who played the brother of Kemp's on-screen character, who had come off worse in an argument with his ex-girlfriend. Though Kemp was sporting a thick lip, his wife denied inflicting it upon him. She said he had suffered an accident while filming and that the whole episode had been nothing more than a "silly row".

Still, it came as no great surprise when she obtained a "quickie" divorce in 2009 on the grounds of his infidelity, which he admitted. By then, she had been introduced to Charlie Brooks, an old Etonian former amateur jockey and trainer and former proprietor of a sex-toy mail-order company. It has been said that they complemented each other perfectly because he has the confidence to make gentle fun of her, saving her from the corporate disease of taking herself too seriously, and because each knows half of the people in the world that anyone ambitious needs to know – so between them they cover the field. Cameron, Gordon Brown, and most of the Murdoch clan were among the rich and famous guests at the couple's wedding two years ago.

They were written up in an immortal article in Vanity Fair shortly before the marriage, which is such a classic of the genre that it is hard to avoid a suspicion that it is a parody. It opened with the words: "When Charlie Brooks wakes up in the mornings in his barn in Oxfordshire, he likes nothing better than to fly to Venice from Oxford airport with his soon-to-be wife Rebekah Wade, the dazzling redhead editor of The Sun, for lunch at Harry's Bar. Later in the day, after shopping and sightseeing, the couple fly back to London for dinner at Wiltons in Jermyn Street."

The article went on to name other members of the "Oxfordshire set" who can reputedly be seen popping in and out of the Brooks' home in Chipping Norton, including Jeremy Clarkson, in whose house the couple first met, Emily Oppenheimer Turner, who sometimes lends them the family home in St Tropez, the Carphone Warehouse boss Charles Dunstone, the Blur bassist Alex James and many more.

In September 2009, after six years of editing The Sun, Brooks stepped up to the post of Chief Executive of News International, at the same time that James Murdoch took over as chairman. This puts her on par with Sly Bailey, of Trinity Mirror, as the most powerful woman in the British media.

As she settled into her new job, the phone-hacking scandal started to bubble up. News International had thought it dealt with it in 2007, when the News of the World royal correspondent Clive Goodman and the private investigator Glenn Mulcaire went to jail, Coulson resigned the editorship and the company convinced the Press Complaints Commission that it had all been an aberration involving one rogue reporter. As that story started to look threadbare, Coulson was compelled to fall on his sword for a second time, leaving Downing Street in January this year.

In March, James Murdoch was called to New York to work alongside his father, in what looked like a News International equivalent of taking the last helicopter out of Saigon. Brooks was left behind in the besieged Wapping Fortress to deal with the biggest scandal to hit the Murdoch media empire.

Despite the calls for her to reconsider her position – from the Dowlers' lawyer, the Labour leader Ed Miliband, politicians and the public – the toughie from Cheshire means to hang on in there for as long as Murdoch wants her to. And he is showing no inclination to cut her loose.

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