Everson leaned in. And so, for the past six months, she’s been leading Facebook Europe, Middle East and Africa (EMEA) in addition to doing her main job as Facebook’s VP of Global Marketing Solutions.Nothing is easy when you’re in charge of Facebook’s most important ad clients—Fortune 500 companies like Unilever and Coca-Cola —while searching for a permanent EMEA boss and caring for young twin daughters. But the payback can be big, as Everson, 41, explained at Fortune Most Powerful Women: London. She told 100 women leaders at our Monday conference that she learned these lessons from temping in London:

1. Humanize the brand. When Everson arrived in London in January, “what I was surprised about was the perception of the Facebook brand,” she admitted. “Clients would say to me, ‘You know, the materials that you use in your presentations–the way you talk about the brand–it’s just not humanizing.” Jumping to fix clients’ perceptions of Facebook, she directed her team to alter their pitch. “Facebook has all of the people that matter to you, where they discover what matters to them,” says Everson, summing up the new, more human Facebook “sell.” She also created a UK advisory board, a twist on a “global client council” that she assembled after joining Facebook two years ago. “They have really become our internal board of directors,” says Everson about the advisory boards. The members are key advertisers. “I actually think it’s an interesting model for all industries,” she says, adding, “Every company has their board of directors. I think every person should have their own personal board of directors.”

2. Safeguard your reputation. “We receive about 4.5 billion pieces of content a day on Facebook,” Everson said when asked how Facebook handled charges that it allows gender-based hate speech. She recalled being with John Hayes, the chief marketing officer of American Express , at a Procter & Gamble conference in May when activists and advertisers pressured Facebook to reform. “He pulled me aside and said, ‘Carolyn, one bit of advice for you: Brands are judged by how they react. Just remember that. If you take every proactive step to fight this, get the content down, put strict policies in place, get more people to actually review the content to protect advertisers.’” Facebook followed Hayes’ advice. “No one, not one digital company, can guarantee anybody that this is going to be a perfect solution,” Everson says about Facebook’s revised guidelines on cyber-hate. “We’re trying to get darn close.”

3. Lean in.
After six years at Viacom’s MTV Networks, Everson was five months into a big new job at Microsoft when she got word that Sheryl Sandberg, whom she did not know, wanted to recruit her to Facebook. “I said, ‘You have got to be kidding me. I can’t do this.’…I thought about it for maybe 30 seconds and realized that I had always loved Facebook. I had tried to buy Facebook when I was at MTV, so I had been watching the company from the very, very beginning.” Everson told the Fortune MPW audience: “It was a really tough process to get through that decision. And people warned me that it was going to be tumultuous. But it turned out to be the best decision for me.”

This Friday, Everson and her husband and two girls are moving back to the U.S. Yes, she found her replacement. Nicola Mendelsohn, formerly executive chairman at fast-growing London ad agency Karmarama, is Facebook’s new VP of the EMEA region–and a clear sign that Facebook’s laser focus is on advertisers.