The link you cited says,
‘Good morning, ma’am,” a member of the uniformed Secret Service once
greeted Hillary Clinton. “F*** off,” she replied. That exchange is one
among many that active and retired Secret Service agents shared with
Ronald Kessler ...
It's a unverified claim by a Secret Service agent which appears in this book written by Ronald Kessler. The agent didn't provide any evidence to Ronald for the claim (it's a hearsay). And it can't be confirmed since Hillary hasn't admitted it and the book didn't provide any evidence for it. The credibility of the book was questioned in this post:
In a calmer world, Ronald Kessler's second book about the U.S. Secret
Service might have made more waves. In The First Family Detail, there
are salacious details about Bill Clinton's alleged mistress (although
Kessler stops short of actually accusing him of having sex with
another woman), the cringe-worthy mental image of Joe Biden swimming
naked, and a bunch of gossip about current and former protectees. ...
Every book ever written has mistakes. But experts are supposed to get
the main things right, and reporters generally follow through when
someone tells them something. Too often, Kessler seems to have
listened to his sources, written their words down, and then simply
printed as fact their allegations or observations without checking on
them. I find that weird.