Here is some more from Business Insider:
Michèle Flournoy met with Defense Secretary Jim Mattis in December about coming on board as his deputy, but she ultimately turned down the job.
A roundtable discussion in Politico Magazine published on Monday finally reveals why: Her own conscience would have made it difficult.
"When [Mattis] called me to ask me to consider ways to help, I had to give it due consideration," Flournoy told Politico's Susan Glasser. "But I also knew that he needed a deputy who wouldn't be struggling every other day about whether they could be part of some of the policies that were likely to take shape."
Flournoy, a cofounder of the Center for a New American Security, has served in a variety of top roles within the Pentagon in the past, and was considered a top pick for Secretary of Defense if Hillary Clinton had won. She most recently served during the Obama administration as undersecretary of defense for policy at the Pentagon, a highly-influential job that Mattis is still trying to get filled.
While there may be some policy differences and too many uncertainties about the Trump Administration, one thing is clear - she would have taken a significant pay cut if she switched jobs. In 2014 she made $282,208 at the think tank, but the DEPSECDEF job only pays about $185,000.