Broadwell appears to be cooperating with investigators in an effort to make this go away, to show that she has nothing else to hide, the sources said.
An assistant to Washington lawyer Robert F. Muse told ABC News that Muse is representing Broadwell. Muse works for the same firm as the lawyer who represented Monica Lewinsky.
Petraeus could possibly face military prosecution for adultery if officials turn up any evidence to counter his apparent claims that the affair began after he left the military.
A friend of Petraeus, retired U.S. Army Col. Steve Boylan, told ABC News, that the affair began several months after his retirement from the Army in August 2011 and ended four months ago.
Broadwell, 40, had extraordinary access to the 60-year-old general during six trips she took to Afghanistan as his official biographer, a plum assignment for a novice writer.
As the details of the investigation launched by the FBI unraveled this weekend, Kelley's name emerged.
Kelley and her husband are longtime supporters of the military, and six months ago she was named "Honorary Ambassador to Central Command" for her volunteer work with the military. Officials say Kelley is not romantically linked to Petraeus, but befriended the general and his wife when he was stationed in Florida. The Kelleys spent Christmases in group settings with the Petraeuses and visited them in Washington D.C., where Kelley's sister and her son live.
"We and our family have been friends with Gen. Petraeus and his family for over five years." Kelley said in a statement Sunday. "We respect his and his family's privacy and want the same for us and our three children."
Earlier this year, around the time that Petraeus and Broadwell were breaking off their affair, Kelley began receiving anonymous emails, which she found so threatening she went to authorities, officials have said. The FBI traced the messages to Broadwell's computer, where they found what one official described as salacious and explicit emails between Broadwell and Petraeus that made it clear to officials that the two were carrying on an affair.
An official told ABC News the FBI uncovered "hundreds if not thousands of emails between Petraeus and Broadwell," many of them salacious in nature.
ABC News' Sarah Parnass and the Associated Press contributed to this report.