The seven women, best friends since North Miami Beach High, gathered for a 40th birthday weekend at a beach resort a couple of years ago.

“No husbands, no children, girls only,” recalls Eve Greenbarg-Albright, one of the seven.

They talked about kids, family, work. They ordered take-out food or made pizza. “We’d be just as happy with Slurpees, M&Ms and chips,” says Greenbarg-Albright.

An unremarkable bonding weekend for old friends — except for the location, which remains a closely guarded secret. When one of the seven friends is Sheryl Sandberg — No. 2 at Facebook, Forbes-ranked fifth most powerful woman in the world and likely to become a billionaire when Facebook’s stock goes public this year — privacy becomes paramount.

Greenbarg-Albright will say only this: The resort is “somewhere in Mexico.”

Sandberg, 42, has reached the heights of success in business while still finding time to speak about the need for women to support each other. And that’s what she practices, too, maintaining a circle of women friends from middle and high school in North Miami Beach, their relationships forged while riding bikes or camping out for concert tickets. Smart and accomplished in their own right, they have remained close for as long as three decades, as Sandberg moved from Harvard grad to the Treasury Department, to Google and now Facebook.

“To understand Sheryl, you have to look at this core group of female friends,” says Brad Meltzer, a best-selling thriller writer who was a year behind them at North Miami Beach High and knows all seven. “They’re smart, dynamic women who have always supported each other. ... It’s a rare thing to have friends who are so close for so long.”

One of the group, Elise Scheck Bonwitt, a Miami-Dade lawyer and mother of five, says Sandberg’s support of women is “just her carrying out what we had in our relationships in high school.”

Some things have changed. Once the women kept in touch by forwarding round-robin letters via the U.S. Postal Service. Now they have a private space on Facebook. All are married. All have kids. A quarter-century after high school, they still get together once or twice a year, “but it’s harder than it used to be,” says Scheck Bonwitt, as the group juggles work and families.

Sandberg isn’t talking to journalists right now; a public relations agency says Facebook executives are in a “quiet period” required by federal regulators as the company prepares for the initial public offering of its stock in the next few months, a move expected to generate $5 billion.

Friends believe the foundations for Sandberg’s stunning success are rooted in her South Florida years. As second in command to Facebook company creator Mark Zuckerberg, she’s become known as the steadying influence on a company filled with brilliant, mercurial entrepreneurs without a lot of organizational or people skills. Fifteen years older than Zuckerberg, she’s considered a personable, smart and efficient manager who has helped the company grow dramatically. Since she arrived four years ago, Facebook has gone from 130 employees to 2,500, from 70 million users to more than 800 million.

Her North Miami Beach friends say she’s extremely bright, commanding, with a way of connecting. “Driven and motivated,” says Greenbarg-Albright. “When she walks into a room, she is very confident.”