It was only later, when she was a freshman at University of California, Berkeley, that Ms. Castro read a news article and realized that Laurene was Silicon Valley royalty, the wife of Apple’s co-founder, Steven P. Jobs.

“I just became 10 times more appreciative of her humility and how humble she was in working with us in East Palo Alto,” Ms. Castro said.

The story, friends and colleagues say, is classic Laurene Powell Jobs. Famous because of her last name and fortune, she has always been private and publicity-averse. Her philanthropic work, especially on education causes like College Track, the college prep organization she helped found and through which she was Ms. Castro’s mentor, has been her priority and focus.

Now, less than two years after Mr. Jobs’s death, Ms. Powell Jobs is becoming somewhat less private. She has tiptoed into the public sphere, pushing her agenda in education as well as global conservation, nutrition and immigration policy. Just last month, for example, she sat down for a rare television interview, discussing the immigration bill before Congress. She has also taken on new issues, like gun control.

“She’s been mourning for a year and was grieving for five years before that,” said Larry Brilliant, president of the Skoll Global Threats Fund who is an old friend of Mr. Jobs. “Her life was about her family and Steve, but she is now emerging as a potent force on the world stage, and this is only the beginning.”

But she is doing it her way.

“It’s not about getting any public recognition for her giving, it’s to help touch and transform individual lives,” said Laura Arrillaga-Andreessen, a philanthropist and lecturer on philanthropy at Stanford who has been close friends with Ms. Powell Jobs for two decades. She is also the daughter of a wealthy real estate developer in Silicon Valley and the wife of Marc Andreessen, the venture capitalist.

“If you total up in your mind all of the philanthropic investments that Laurene has made that the public knows about,” she said, “that is probably a fraction of 1 percent of what she actually does, and that’s the most I can say.”

While some people said Ms. Powell Jobs should have started a foundation in Mr. Jobs’s name after his death, she did not, nor has she increased her public giving.

Instead, she has redoubled her commitment to Emerson Collective, the organization she formed about a decade ago to make grants and investments in education initiatives and, more recently, other areas.

“In the broadest sense, we want to use our knowledge and our network and our relationships to try to affect the greatest amount of good,” Ms. Powell Jobs said in one of a series of interviews with The New York Times.

Still, the fortune she inherited, making her the world’s ninth wealthiest woman, according to the Bloomberg billionaires index, has catapulted her into the upper echelon of global philanthropists. And that has led to certain expectations.

Ms. Powell Jobs has a net worth estimated at $11.5 billion, according to Bloomberg, most of it in shares of the Walt Disney Company. Mr. Jobs helped found the animation studio Pixar, which Disney acquired in 2006 and paid for in stock. With 131 million shares, worth about $8.7 billion, the Laurene Powell Jobs Trust is Disney’s largest shareholder with a 7.3 percent stake in the company, and she has benefited from the stock having more than doubled since her husband died in October 2011.

Mr. Jobs also owned 5.5 million shares of Apple at the time of his death, and it is unclear whether she has sold her position.

“She knows that she is in an unusual position and has the standing to have a major impact on the world stage,” said Peter Seligmann, chief executive of Conservation International, on whose board Ms. Powell Jobs sits. “It will be fascinating to watch the choices that she makes.”

Like many technology titans, her husband was criticized for not giving away as much money as he could. Mr. Jobs did not give publicly during his life — though there have been rumors of at least one major anonymous gift, to a hospital.