NEW YORK – “How could this happen?”

For many, that was the inevitable question Tuesday in response to the news that Dana Reeve, the sunny and vibrant widow of Christopher Reeve, had died of lung cancer at the stunningly young age of 44.

It’s not that people didn’t know the statistics – most people know a diagnosis of lung cancer is devastating. But the image Reeve projected publicly – and lived privately, according to those who knew her – was so upbeat and resilient that people simply couldn’t fathom she was gone, only months after being diagnosed.

Along with the shock of her death came deep sadness for her 13-year-old son, Will, who now has lost both parents in less than 18 months.

“Once you become a parent,” said Susan Solovay, a mother of two in New York City, “the scariest thing you can imagine – outside of the obvious health issues for your child, or kidnapping – is leaving your child too soon. You think, who will love and take care of them the way I have?”

Elaine Friedman, also of New York City, learned of Reeve’s death on the morning news. “I felt so terribly sad,” she said. “It’s not just that she was so young. It’s that she’d had so much tragedy already, with her husband. And then she gets diagnosed with lung cancer, and she wasn’t even a smoker.

“In a way,” Friedman said, “it seems to some degree that she died of a broken heart. It made me think that maybe she went to join him.”

A similar shock wave greeted the news in August that Reeve, who won huge admiration with her tireless support of her husband during his nine years as a quadriplegic, had been diagnosed. Many expressed surprise that a woman in her 40s who had never smoked could be struck by the disease.

But doctors say one in five women diagnosed with lung cancer never lit a cigarette. Lung cancer under age 45 is rare – only 3 percent of lung cancers occur in that age category, regardless of smoking status – and experts say genes are the main explanation.

Reeve was upbeat about her prospects. “I hope before too long to be sharing news of my good health and recovery,” she said in the announcement of her illness. A private person, she hadn’t wanted to disclose the news even then, but she knew a tabloid was about to.

Then, in November, Reeve appeared at a gala fundraiser for the Christopher Reeve Foundation, for which she was a chairwoman. If the crowd hadn’t known she was ill, they wouldn’t have been able to tell. She looked healthy and energetic in her multihued gown. She wore an attractive, long-haired wig – her one visible concession to chemotherapy.

Onstage, she smiled at the crowd and told them her tumor was “shrinking and shrinking and shrinking.”

“I’m beating the odds and defying every statistic the doctors can throw at me,” she said, to happy applause. Offstage, she cheerfully greeted her high-powered guests: Meryl Streep, Glenn Close, Robin Williams, Diane Sawyer and Mike Nichols, Michael Douglas and Catherine Zeta-Jones.

Friends say Reeve tried to keep her life as normal as possible for her young son, taking trips and picking him up at school when she could.

But sometime after Christmas, her condition worsened significantly, although in mid-January, she belted out Carole King’s “Now and Forever” at the Madison Square Garden retirement ceremony for New York Rangers captain Mark Messier.

Michael Manganello, Christopher Reeve’s former assistant and vice president of the Christopher Reeve Foundation, told ABC.com that Reeve had known for about six weeks that the end was nearing.