She was Rolling Stone’s first female contributing editor, and she’s published two fine books about popular music (Nowhere to Run: The Story of Soul Music and We Gotta Get Out of This Place: The True, Tough Story of Women in Rock), but Gerri Hirshey knows she doesn’t fit the stereotype of the flamboyant, macho rock journalist. “I’m a pretty quiet, shy type,” she says, seated cross-legged on the living room couch of her Upper West Side apartment. “Michael Jackson once said to me, ‘You know, you’re just like me: you get to tap dance on the page, and then nobody can find you and you don’t have to deal with anything.’ I said, ‘You’re absolutely right!’ ”

The subject of Hirshey’s new book, Not Pretty Enough: The Unlikely Triumph of Helen Gurley Brown (Farrar, Straus and Giroux, July), was also a woman who flouted expectations in a male-dominated world. In 1962, when women were told their life’s goal was to get married and make babies, Helen Gurley Brown declared in the scandalous bestseller Sex and the Single Girl that having a career was just as important as marriage and babies, and sex outside marriage was not only not wrong, it was fabulous. The ultra-girly attitude she turned into a trademark as editor-in-chief of Cosmopolitan magazine is easy to make fun of—Hirshey herself parodied a Cosmo girl in a 1980s piece for the New York Daily News—but there was a lot more to Brown than fluttering eyelashes and fishnet stockings.

“My friend [editor and author] Betsy Carter was the one who suggested the bio, and I started looking into it, thinking I knew all about Helen,” Hirshey recalls. “I realized that, like many people, I had no idea about her. It was a very rich American story, with 90 years of women’s history, plus there were live bodies to chase, which made the reporter in me say, ‘Oh, boy!’ ”

Known as the Nutcracker at Rolling Stone for her ability to handle difficult interviews, Hirshey found most of Brown’s surviving friends eager to talk. “It was very much like when I did Nowhere to Run,” she says. “The soul musicians were always on the Tonight Show but never invited onto the couch, and a lot of people weren’t pleased about the lack of access to Helen toward the end (Brown died in 2012 at age 90). Hearst, Cosmo’s publisher, took very good care of her; I do not dispute that, but her real friends had things they wanted to get off their chests.”

Brown’s personal archive at Smith College contained a rich trove of revealing material, including a 1972 interview in which she spoke with far more anger and honesty than she usually exhibited in her coquettish public persona. It was frustrating and baffling, Hirshey says, to be denied permission to quote from it by Hearst, which controls the archive copyrights. The company also forbade current employees to speak with her. “I don’t know why,” Hirshey says. “It wasn’t like I was there to dig up skeletons.”

Asked if Hearst might have been cooperating exclusively with Brooke Hauser, author of the just-published Enter Helen: The Invention of Helen Gurley Brown and the Rise of the Modern Single Woman, Hirshey shakes her head and says ruefully: “I know for a fact she didn’t even approach Hearst; she was smarter than me. She probably experienced a lot less agita than I did.” Whereas Enter Helen focuses on Brown’s career in the 1960s and ’70s, Hirshey devotes roughly half of Not Pretty Enough to Brown’s life before Sex and the Single Girl was published, including her poverty-stricken childhood in Arkansas and years of a variety of crummy jobs in Los Angeles before she found success as an advertising copywriter.

Hirshey explains that “you can’t understand who Helen was unless you know the tragedies and privation of her Southern girlhood.” She adds: “Her ambition was born of desperation. And what I tried to get at in emphasizing her advertising career, which has been shorted everywhere, is that work was as important as sex to her. Work gave her independence and a sense of self-worth.” Brown was driven, Hirshey argues, by the insecurity over her attractiveness that gives the biography its title, and her sense of being “not pretty enough” forged her connection with Cosmopolitan’s readers. “She told them, ‘Make the most of what you’ve got; don’t let ordinariness stand in your way.’ It was aspirational in a realistic way, and the big-sister voice she had was key.”

Writing a substantial biography of a single person was a challenging change of pace for her, Hirshey says. “I’ve always been a short-form biographer; that’s what I was known for in my magazine work.” Her two previous books showcased her ability to nail a personality in a few cogent pages. It was “quite an adventure,” she says about Nowhere to Run, “being out on the soul train, showing up in places like Detroit: I got myself into some situations!” First published in 1984, the book continues to be reprinted all over the world and has some famous fans. “I had no idea that it was on David Bowie’s 100 favorite-books list until after he died,” Hirshey says. “Of course, they’re such freaks for soul music in England; Jagger told me he read it twice, Keith Richards, all those guys. It’s still dear to my heart, as is the music.”

We Gotta Get Out of This Place, Hirshey says, “was more a function of necessity than passion.” She explains: “I had done a women’s issue for Rolling Stone, so I had done a lot of research, and Morgan Entrekin at Atlantic said, ‘Why don’t you do a book?’ At the time, it was the late 1990s, my dad was dying, and I needed something I could stay home with. It worked out personally, and I adored all the women: Ronnie Spector, who is still a dear friend, Dolly Parton, Tina Turner, Cher—I had a ball with them. But it was less a labor of love, and I think you can tell the difference when you read it.”

Such candor is typical of Hirshey, who says bluntly that after more than 30 years of feature articles and columns in big-name periodicals, “I made the decision a while ago that magazine work is just untenable now. The fees and lengths are half what they were, and it’s dumbed down, for websites particularly. I can’t make my peace with other people’s lack of vocabulary at this point, and with a book you don’t have to.” She’s easing into promoting Not Pretty Enough by accompanying her husband, documentary filmmaker Mark Zwonitzer, on the road to promote his new book, The Statesman and the Storyteller: John Hay, Mark Twain, and the Rise of American Imperialism (Algonquin, April). “Our agent said she hates representing a husband and wife, let alone when they have two books coming out at the same time,” Hirshey laughs.

Hirshey says she’s still too exhausted from Not Pretty Enough to think about another book: “I had no idea what I was walking into; I don’t think I would take on anything of this magnitude again. But if something comes along that’s as juicy and intriguing, I’ll see what happens.”