Facebook’s already terrible year is ending on a new low, as Mark Zuckerberg and his beleaguered executive team battle another share price slide, this time triggered by new revelations about the company’s relaxed attitude to the privacy of its 2.2 billion customers’ data.

Shares dropped more than 7% on Tuesday after it was revealed that the company had bent its own data rules for clients including Netflix, Spotify, Amazon, Microsoft and Sony.

The latest damaging report, published by the New York Times on the back of a District of Columbia lawsuit accusing the social media giant of exposing residents to political manipulation by “failing to protect” user data during the 2016 US presidential election, will surely be disagreeable to Zuckerberg, Facebook’s 34-year-old founder, chief executive and controlling stockholder.

But it is Sheryl Sandberg, former chief of staff at the US treasury under Larry Summers and the woman brought in a decade ago to be the “adult” in Facebook’s executive ranks, who is largely taking the heat for the company’s mounting operational, financial, political and public relations challenges.

Clearly, Sandberg has much to account for as chief operating officer. Facebook’s travails, which have seen it shares drop nearly 40% since their July peak, are not Sandberg’s alone to carry, though on some days it appears the 49-year-old has been doing much of the heavy lifting.

“There’s little doubt the company is facing critical challenges and has made some egregious mistakes,” says Kathryn Kolbert of the Athena Centre for Leadership Studies. “The fact that Sandberg was brought in to be the adult in the room does not absolve Zuckerberg of responsibility.

“Mark Zuckerberg is the CEO of a multibillion-dollar company, and he’s been at it a while. He’s a grown-up. He ought to be responsible. But from what I see, there isn’t the sense that both should be accountable.”

Five weeks ago, Sandberg’s key role in shaping the company’s response to multiple crises was exposed, again by the New York Times. These have included the revelations of Russian interference in the 2016 election, the Cambridge Analytica scandal, and the decision to hire a rightwing opposition research company, Definers Public Affairs, to apply aggressive political campaign tactics to Facebook’s PR and to look into the finances of high-profile investor George Soros days after he publicly criticised the big US technology companies.

Facebook claimed that the research into Soros “was already under way when Sheryl sent an email asking if Mr Soros had shorted Facebook’s stock”.

However, the backlash against Sandberg, until recently a figurehead for tech-branded progressive feminism, has barely relented.

The bestselling author, who just a year ago was riding high on the success of Option B, a follow-up to her empowerment manual Lean In, is taking hits from all sides.

Sandberg, as the executive who helped develop Google’s ad-supported business strategy before joining Facebook, was in the firing line in September when the company became the focus of an American Civil Liberties Union complaint alleging that its advertising system allows employers to target job ads based on gender.

Three weeks ago, before a sold-out audience at the Barclays Centre indoor arena in Brooklyn, former first lady Michelle Obama said Sandberg’s belief that women can always “have it all” if they assert themselves across their personal and professional lives – a key tenet of Sandberg’s Lean In philosophy– is “a lie”.

“It’s not always enough to lean in because that shit doesn’t work all the time,” Obama reportedly said.

Then last week the civil rights group NAACP launched a week-long boycott of Facebook after a report it had commissioned highlighted concerns over voter suppression, ad targeting and the company’s own issue with workplace diversity.

“We know that we need to do more: to listen, look deeper and take action to respect fundamental rights,” Sandberg said in a conciliatory statement.

According to Nathalie Molina Niño, author of Leapfrog: The New Revolution for Women Entrepreneurs, part of the hostility aimed at Sandberg is certainly related to her gender. “The higher a woman gets in terms of success, the greater the culture that enjoys taking her down,” Niño says. Indeed, negative posts on Sandberg’s own Facebook page are largely written by men.

At the same time, Niño points out, Lean In missed the mark because it failed to reflect the experience of most women who are balancing work and family.

As a result, Sandberg has become synonymous with a particular brand of female empowerment that is considered out of touch with notions of inclusiveness.

“It’s applicable only to women in the corporate world and that’s a fairly small, marginal group,” Niño says. What Lean In showed, in fact, “is in contrast to what is true for most women, and the backlash against Sandberg is a reflection of that reality”.

But Sandberg is not standing back. It is a measure of her resilience, as well as solid support from Zuckerberg and Facebook’s board, that she has stayed put.

In an interview with the news network CNN, Zuckerberg said: “Sheryl is a really important part of this company and is leading a lot of the efforts to address a lot of the biggest issues that we have. She’s been an important partner for me for 10 years ... I hope that we work together for decades more to come.”

While Sandberg is taking the heat for Facebook’s problems, Zuckerberg appears to be relatively unscathed. “The company is facing incredible challenges and has made egregious mistakes, so Zuckerberg should bear primary responsibility,” says Charles Elson, expert in corporate governance at the University of Delaware.

Forcing Sandberg out, he says, would solve the perception that the company is taking action, but achieve nothing in terms of resolving the seemingly insurmountable issue of policing the user content of a global social network.

“The public wants somebody to take the fall, and since Zuckerberg is the owner he’s not going to do it. So they’ve come to the view that Sandberg is the next best thing.”

But that risks a potential new PR backlash by pushing Sandberg out without solving any of the company’s data privacy and political manipulation issues.

If Sandberg departs, her brand too tarnished to be of further use to Facebook, the decision will be Zuckerberg’s to make. “As the majority voting shareholder, he calls the shots,” Elson points out.

Facebook’s terrible year

17 March
The Observer and New York Times reveal that Facebook accidentally allowed consulting firm Cambridge Analytica to gather members’ data for political purposes. The number of users is later put at 87 million.

10-11 April
Founder Mark Zuckerberg testifies before the Senate judiciary and commerce committees. He says Facebook “didn’t take a broad enough view of our responsibility, and that was a big mistake”.

3 June
The New York Times reports that Facebook struck agreements allowing phone-makers including Apple, Amazon, BlackBerry, Microsoft and Samsung to access users’ personal information.

26 July
Facebook’s share price plunges 20%, wiping $17bn off the value of Zuckerberg’s stock, after the company reveals that 3 million European users have quit.

5 September
Sandberg testifies before the Senate intelligence committee regarding efforts to prevent foreign states from spreading false information on social media.

28 September
Facebook announces that hackers used 400,000 accounts under their control to gain the access tokens of nearly 50 million Facebook users, in the firm’s largest data breach.

14 November
The New York Times reports alleged tactics by the firm to block scrutiny of Russian disinformation and hate speech distributed via Facebook.

15 November
Facebook creates an independent body to monitor offensive content. Zuckerberg says he now believes that Facebook “should not make so many important decisions about free expression and safety on our own”.

21 November
Facebook confirms it hired rightwing political research firm Definers Public Affairs to attack George Soros and undermine critics by publicising their links to him. Zuckerberg and Sandberg deny knowledge of the arrangement.

30 November
The New York Times reports that Sandberg asked Facebook communications staff to research Soros’s financial interests after he describes social media, and Facebook in particular – as “a menace to society”.

18 December
Maryland sues Facebook, claiming it failed to safeguard users’ data, exposing nearly half of the District of Columbia’s population to potential “manipulation for political purposes”.

18 December
The New York Times reveals that Facebook shared user data with other tech giants more widely than previously known in a push for faster user and advertising growth.