The article is right that Michelle Flournoy likely becoming the next Secretary of Defense was not a well kept secret:

Flournoy founded the Center for a New American Security think tank and led it for several years. 

On June 20, 2016, then-Vice President Joe Biden delivered keynote remarks at an event hosted by the Center for a New American Security, the think tank founded and, at that point, led by Michèle Flournoy.

Flournoy introduced Biden, praising him as a national security thinker and noting the ties between his staff at the White House and CNAS. Biden, in turn, acknowledged the little-kept secret of the defense world: that Flournoy was in line to become the first woman to serve as defense secretary under President Hillary Clinton.

“Well, madam secretary,” Biden said with a laugh as the crowd applauded. “I’m writing a recommendation for her, you know.”

The Clinton administration never materialized, following the election of President Donald Trump. But four years later, president-elect Biden is widely expected to fulfill his promise and tap Flournoy to lead the U.S. military.

Defense News

You can read more at the link, but supposedly Tammy Duckworth is interested in the position as well. Flournoy is way more qualified especially when you consider the difficulties Duckworth had running the Illinois VA. What creates confidence that she could run a much larger organization like the Pentagon?