Dna, photos, video, recordings, emails, cards, letters: all would be "witnesses" that could bear testimony to her veracity.
Her son; hotel staff, airline staff, restaurant staff, or other incidental third parties: 13 years of a relationship like she described doesn't occur in a vacuum. Someone would have seen something to corroborate her story.
Monica? Blue dress with semen stains that carried Bill's DNA; Monica herself told at least one backstabbing "friend" who outed her; then other evidence began to emerge.
Kennedy? WHICH Kennedy?!? Bobby, Teddy, or John? Or Patrick? Or Old Man Joe? Or the Kennedy cousin, Michael Skakel? Or William Kennedy Smith?
Barney Frank? That poerful congresscritter who is a member of a protected class, whose buddies and roommates took falls, while he remained unscathed?
As I’m sure you know, there is a difference between witnesses and evidence.
The post of yours that I quoted called for witnesses.
I guess (spelling it out) that one has no more witnesses to one-on-one interactions with any of the other folks that I brought up than you would in any other situation, but it is still believed (fairly) that they were involved in them.
And I’d suggest you believe it, too. Even without other witnesses.