FORTUNE — Ellen Kullman had her game plan ready. She was set to take over as the first female CEO of DuPont in January 2009 with about two decades of experience at the chemical giant behind her.

“Then Lehman crashed, and you throw the plan out the window,” Kullman said at Fortune’s Most Powerful Women Summit on Tuesday.

Kullman developed a new playbook that would get the company through economic turbulence but also put an even greater focus on emerging from the financial crisis stronger than ever. For guidance, Kullman read up on DuPont’s 209-year history to see how the company had survived previous struggles.

One area Kullman refused to alter: “We did not cut research and development,” she says. “That’s our lifeblood.”

Kullman noted that the agricultural sector didn’t go through a financial crisis, which helped create a cushion for DuPont (DD). She’s since further positioned the company as a food and nutrition business with the recent $6.4 billion acquisition of Danish enzyme maker Danisco.

Her management helped turn DuPont from what interviewer and Fortune Assistant Managing Editor Leigh Gallagher described as a lumbering giant that had drifted from its roots into a stock market turnaround story.

Kullman says 2010 was a tremendous year because volumes returned after the abysmal 2009, but today’s economic uncertainties have slowed growth. Rather than implement a general strategy, she said that this is the type of environment where executives must look at every sector and country to set the right path.

One of the major issues in the U.S. is that more scientists, engineers, and information technologists are needed. “There are jobs open in our country today that we can’t find skilled workers for,” said Kullman, who started out as an engineer.

To get the next generation interested in the sciences, she says perceptions have to change. People become doctors because they want to help people, not because they like biology, she says. It’s the same with science, which isn’t about being hard, she adds. “It’s about solving problems.”

Check out our additional coverage from Fortune’s Most Powerful Women summit.