The intensive session, like so many before it for Ms. Williams, was aimed at prepping the rapper for his first full day of glad-handing media outlets. The record label had brought in its secret weapon: a well-connected industry veteran with a voice like aloe vera and a maternal mien.

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Summing up Ms. Williams’s bona fides, Gabe Tesoriero, Def Jam’s executive vice president of media and a longtime publicist for Kanye West and Justin Bieber, cited a line about the Grateful Dead: “They’re not the best at what they do,” he said, “they’re the only ones who do what they do.”

A throwback to the days of Berry Gordy’s Motown and its etiquette coach Maxine Powell, Ms. Williams, who said she was paid hourly “like a lawyer — a high-end lawyer,” has spent more than two decades as a freelance media adviser and strategist for just about every prominent label and artist management team. From the embryonic stages of Rihanna and Mr. Bieber’s careers to the ups and downs of D’Angelo, Ms. Williams has been in the background with tips, encouragement and, when necessary, a healthy dose of what the hell are you doing?

She has testified on behalf of Meek Mill, had an unfruitful meeting with Mr. West after his Taylor Swift V.M.A.s moment (“I don’t need any coaching,” he told her), and warmed up T.I. for his 2010 post-prison tell-all interview on “Larry King Live.” Beyond the record business, there have been C.E.O. clients and athletes like Michael Vick and Allen Iverson, but music has remained Ms. Williams’s core.

And while her pupils have spanned genre (members of the Dave Matthews Band, Pete Wentz, Pitbull), young black artists have been a focus, with more and more neophytes coming to Ms. Williams as the industry doubles down on rap and R&B, much of it emerging raw from the depths of the internet.