Rosalind Wiseman regularly receives emails from women who think they are going to surprise her with the following divulgence: “You are never going to believe this: My work is like middle school.”

Ms. Wiseman, however, is unfazed. “Of course I can believe it,” she said. Her response is a pep talk that goes something like this: “I remind them that they aren’t weak because they are affected by these dynamics. And that even if we have left our teen years behind us, we are driven to feel valued by the groups we are connected to, and most of us will do anything to avoid embarrassment and shame. It’s not an opportunity to lash out at people in retribution, no matter how horrible the other person is.”

Women decades past high school seek out Ms. Wiseman because they know her as the author of “Queen Bees and Wannabes: Helping Your Daughter Survive Cliques, Gossip, Boyfriends and Other Realities of Adolescence,” the inspiration for the 2004 cult classic “Mean Girls.” The film brought Ms. Wiseman’s taxonomy of girl clique roles — the queen bee, the banker (the supplier of gossip) and the sidekick — to the big screen, and it comically portrayed a set of behaviors that Ms. Wiseman argued were pervasive among girls and women yet lacked definition and social validation.

Though the mean girls in Tina Fey’s films haven’t grown up — the adaptation of the “Mean Girls” musical, out on Jan. 12, is set in high school, too — Ms. Wiseman’s have. These days, she spends the bulk of her time on the global speaking and consulting circuit, working with schools, government agencies and corporations. Her clients have included the State Department, UBS Financial Services and the M.I.T. Media Lab. Fifty percent of her work, Ms. Wiseman says, is with adults.

It may feel a bit dismal — or even retrograde — to be talking about mean girls in 2024. Female camaraderie seems to be the order of the day, fueling cultural phenomena like Taylor Swift’s billion-dollar Eras tour and the box-office bonanza of Greta Gerwig’s “Barbie” movie. The #girlboss movement and Sheryl Sandberg’s “Lean In” feminism tried to empower women in the workplace, and “shine theory” emphasized the importance of lifting up other women along the way to career success. But it turns out that there’s still a lifetime of deep-rooted social conditioning to undo, according to Ms. Wiseman.