Secret mistress? LOL
It was no secret in Washington that she was JFK’s mistress.
It was no secret in Washington that the CIA had her bumped off. Her former husband, Cord Meyer, was CIA. Her brother-in-law was Ben Bradlee. She supplied JFK with LSD and a few other things. She knew too much and talked too much.
Depends on what you mean by "Washington." A lot of politicians and reporters didn't have a clue what was going on. Some of those who thought they did, didn't know names and details. And people could keep different and conflicting ideas in their mind at the same time so long as they didn't have any definite evidence, so some who sort of "knew" about Jack's sex life didn't really "know."
she had become very vocally anti-CIA, too
not only loose with sensitive matters but harshly against the agency
she sure could have stepped on the wrong toes at some of those DC cocktail parties