Not long ago, Shannen Doherty, the once and future Brenda Walsh, took a day off from shooting the short-lived TV show North Shore in Hawaii and went on a shark-diving trip with a couple of friends. Hundreds of yards offshore, Doherty descended into the water in a protective cage. Members of the boat’s crew chummed the water, sharks gathered—and Doherty freaked.

“I couldn’t breathe, I started having an anxiety attack, I couldn’t stay out of their reach,” Doherty says, shuddering. Her Irish brow crinkles into slight worry lines that make her look her age, which is 37. “They were slamming into the cage—they looked so frickin’ mean! My leg slipped a little through the bars, and a shark swam up against me and rubbed off a layer of my skin.”

Doherty is telling the story in a restaurant on the Pacific Coast Highway, in Malibu, a few hundred yards from the beach. She still owns nine or ten surfboards but hasn’t been on one—or even swum in the ocean—since the shark encounter. “I tell myself the least I can do is give the ocean back to the sharks,” Doherty says. And then she giggles. “No, that’s just a bullshit rationalization—I’m just terrified now.”

Doherty, who’s reprising the role of Brenda on the CW’s revival of 90210, could look at her shark-cage experience as an apt metaphor for her twenties—not-so-tender years marked by catfights, nude photo spreads, a turn leading the Pledge of Allegiance at the 1992 Republican National Convention, and a slew of ill-chosen male companions. Her eyes widen when she’s presented with the parallel. “I never thought of that before,” she says. “And now I’m playing Brenda again. Wow.”

Doherty lets the concept sit a moment before elaborating: “Well, I’ll go to the beach and I’ll wade up to my knees. But I’m not going to start swimming again.”

Shannen Doherty may not have been a nice girl, but she is a sweet woman. Then again, there is nowhere to go but up after you’ve singlehandedly defined the modern American mean girl.

The journey began with her performance in 1989’s Heathers, as the quiet yet lethal member of the troika of button-nosed title characters. But Doherty went hard-core after she was cast on Beverly Hills, 90210, which made its debut in 1990. As Brenda Walsh, she played a virginal daughter of Minnesota relocated to the zip code of the entitled and wealthy. Brenda was initially a likable, naďve beauty, but her equanimity didn’t last long: she soon morphed into Elizabeth I in Guess jeans, adopting a kill-or-be-killed attitude toward all of teendom. Kurt Cobain’s refrain “Here we are now, entertain us” might have captured the nineties Zeitgeist, but so did Brenda’s Season 2 bon mot, “To be a bitch or not to be a bitch—that is the question.”