The news is shocking, not just because Barnes is only 56 years old. She has always looked and seemed younger than her years. And while she always has taken her job seriously, she has never taken her position too seriously for her own good.

Barnes, who ranks No. 10 on Fortune‘s Most Powerful Women list, has never gotten consumed by her career. Or at least when she did, she did something about it. This is the woman who famously, in 1997 after 22 years at PepsiCo , quit her job as CEO of Pepsi-Cola North America to be a better mom. Being the most powerful woman in the consumer-goods industry–which she was, based on revenues–didn’t matter as much as being there for her three kids.

A year later in 1998, Fortune put Barnes, then 44, on its inaugural MPWomen list, at No. 44. Even though she lacked a 9-to-5 executive gig, she turned herself into one of America’s most desired corporate directors. She joined the boards of Avon , the New York Times , Sears , George Lucas’ Lucasfilm, Staples and Starwood Hotels , where in a management pinch, she stepped up to interim president, reluctantly.

All the while, Barnes was scanning the corporate universe to determine where she might eventually return in a full-time position. Living in Illinois, where she grew up, she also taught for a while at Kellogg Graduate School of Management. I recall going to speak to her class, and Barnes telling her students that the time to consider changing a career is when you don’t desire a move up to the next-highest position.

She ended up joining Sara Lee in 2004 as president and COO and moving up to CEO a year later. She knew she faced a huge challenge, remaking a consumer conglomeration that sold everything from Hanes hosiery to hot dogs. But amidst the recession and spikes in commodity costs, it’s surely been more difficult than she had envisioned. After selling billions of dollars worth of assets and cutting the workforce, Sara Lee stock is down 35% from February 2005, when she took over.

Even with friends, Barnes is intensely private. So it’s not so surprising that neither she nor Sara Lee is disclosing how serious her stroke was or whether she’s likely to return to the company. The company announced this morning that it will give an update on or before its August 12 end-of-year earnings call.

“She’s recuperating and on the mend,” Sara Lee communications boss John Harris told me today. “Recovering from a stroke can be a very long process,” he added. When he spoke with Barnes last week, he said, she was in “good spirits.”

That’s encouraging. Barnes’ three children, two sons and a daughter, have been helping her through her ordeal. We wish her a fast and full recovery.