Marilyn Tavenner, the head of the federal agency that oversaw the rocky HealthCare.gov rollout, announced Friday she was stepping down from her post.

Tavenner, in a lengthy email to staff, did not give a reason for her departure, scheduled for the end of February. She said she is leaving as head of the Centers for Medicare and Medicaid Services with “sadness and mixed emotions.”

Tavenner's last two years in Washington were chaotic, encompassing both the rush to launch the federal website for the ObamaCare exchanges, and the fierce recriminations that followed when the site stumbled out of the gate in October 2013. Though she stayed in the position despite the widespread technical glitches, she faced tough questions on Capitol Hill. 

More recently, she came under fire for exaggerating the number of people who had enrolled for Affordable Care Act coverage. Tavenner told Congress that 7.3 million were enrolled, which was inflated by about 400,000.

Health and Human Services Secretary Sylvia Burwell said the decision to leave was Tavenner’s. 

Rep. Darrell Issa, R-Calif., former chairman of the House oversight committee, said in a statement that Tavenner "had to go." 

He said: "She presided over HHS as it deceptively padded the Obamacare enrollment numbers. It was a deplorable example of an agency trying to scam the American people. They weren't successful this time because of Congressional oversight. We deserve better."

Republican Sen. Orrin Hatch, of Utah, though, said in a statement he was sorry to see Tavenner go.

“She has proven herself to be a strong leader and a straight shooter who brought in much-needed private sector sensibility into the agency," Hatch said in a statement. "I truly appreciate her service and wish her the very best in her next adventure." 

Accounts have emerged since the HealthCare.gov launch showing the drama behind the scenes in 2013. 

In November, as FoxNews.com previously reported, an email surfaced alleging Tavenner used threats and tantrums to ensure HealthCare.gov launched on time. The email from Michelle Snyder, formerly the second-ranking official at the Centers for Medicare and Medicaid Services, said Tavenner engaged in a “cruel and uncaring march” to launch the federal health care website on time.

“Just so you know [Tavenner] decided in January we were going no matter what,” Snyder wrote in the email. Snyder added that Tavenner “threatened me with a demotion or forced retirement if I didn’t take this on.”

In the September 2013 email that was sent to Todd Park, the former chief technology officer of the U.S., Snyder said Tavenner didn’t grasp what was at stake.

“Do you really think [Tavenner] has enough understanding of the risks to fight for a delay — no and hell no,” she wrote.

Tavenner will be replaced by Andy Slavitt, a former executive at UnitedHealth Group, who has worked with the agency on HealthCare.gov’s technical issues.

Slavitt will ultimately need a Senate confirmation if he is to be Tavenner’s permanent replacement.