When Ellen Kullman stepped into the CEO role at DuPont this month, she became the 13th female Fortune 500 CEO. That’s a milestone. But Kullman’s ascension passed with little fanfare. She addressed employees in a year-end video on DuPont’s intranet site but has yet to address them as a group or to send out a company-wide email since the start of the year.

Why so quiet? Well, unlike a lot of power shifts these days, Kullman’s promotion was neither controversial nor surprising. On the day last September when her predecessor, Chad Holliday, announced that Kullman, 52, would succeed him, we were just finishing our 50 Most Powerful Women in Business list (see Pattie’s post about Kullman from September) and we had already yanked Kullman up 10 slots to No. 15. That’s because her promotion seemed inevitable. She already had responsibility for four of DuPont’s five product platforms. She’s also popular with the rank and file. A 20-year DuPont veteran, Kullman began her career as marketing manager in medical imaging.

Now she must hit the ground running. DuPont stock is down 43% to $26 since she was named CEO-designate. Meanwhile, the S&P has dropped 25%. In early December, in her 2009 strategy update for investors, Kullman talked about sharp demand declines, workforce reductions, and other cost-cutting measures. Where’s the growth? In DuPont’s agriculture business, she said, plus photovoltaics, biofuels, and safety and protection products – likely to benefit from government stimulus projects in infrastructure around the globe.

It’s a good thing Kullman has given up the seat on the General Motors board she’s held for four years. Can you even imagine helping to steer GM through its survival while cutting your teeth as CEO of a complex company with $31.6 billion in revenues last year?

One more responsibility Kullman has declined: being the direct boss of her husband. Michael Kullman is still marketing director of innovation at DuPont and reports to chief science and technology officer Uma Chowdhry. Chowdhry reports to EVP Tom Connelly, who reports to CEO Ellen Kullman.