Ms. Broadwell is the author of a biography of the general, and she's reportedly under investigation.
From Fred Kaplan, at Slate, "Petraeus Resigns Over Affair With Biographer" (viaMemeorandum):
The woman with whom Gen. David Petraeus was having an affair is Paula Broadwell, the author of a recent hagiographic book about him, All In: The Education of General David Petraeus.And then from NBC's Richard Engel, "Petraeus' biographer Paula Broadwell under FBI investigation over access to his email, law enforcement officials say." Engle does not mention Broadwell as the mistress, but has this:
Broadwell's Twitter account describes her as a national security analyst and Army veteran. A biography on her website, which went offline Friday evening, said she is married to a radiologist and has two children, both boys. The family lives in Charlotte, N.C. The biography said she is a West Point graduate and a research associate at Harvard University's Center for Public Leadership and a doctoral candidate in the Department of War Studies at King's College London.More at the Wall Street Journal, "CIA Chief Resigns Over Affair" (viaMemeorandum).