April 01, 1996 12:00 PM

ROSALYN MCMILLAN HAS ALWAYS had plenty of reasons to thank her sister Terry. During their childhood in Port Huron, Mich., Rosalyn remembers, it was Terry, older by two years, who “took care of my brother and two sisters and me,” easing the burden on their factory-worker mother. “Terry cooked, washed our hair and made sure we got our homework done,” says Rosalyn, 42. “I was so proud of her—I wanted to go everywhere she went.”

Lately, it looks as if she just might, and Terry has played a part in that too. It was after a 1991 phone conversation with her sister (whose novel Waiting to Exhale was poised for blockbusterdom the following year) that Rosalyn, then a car seat-cushion seamstress at a Mount Clemens, Mich., Ford plant, sat down at her computer. “Terry said few novels by African-American women had been published that year,” Rosalyn says. “I thought, ‘Maybe I could write one.’ ” Her first novel, a blue-collar romance titled Knowing, has just been published to generally positive reviews (“Enthralling,” pronounced an ENTERTAINMENT WEEKLY critic) and is already in its third printing.

But sisterhood isn’t all-powerful, and—as Terry will be the first to admit—Rosalyn is no mere coattail rider. “She’s a go-getter,” Terry says. Rosalyn refused Terry’s offers of help on the novel. “She’d call and ask, ‘How’s the book going, Booge?’ ” says Rosalyn, who got the nickname in childhood. “I’d let her know I was working on it, then she’d let me go on my merry way.” And when it came time to find an agent, Rosalyn didn’t trade on Terry’s name. “McMillan’s a fairly common one, so the connection never occurred to me,” says Detroit-based agent Denise Stinson (who did mention the tie when she landed Rosalyn a five-figure deal with Warner Books).

Writing is something McMillan has felt she could do since childhood. Back in Port Huron, money was perpetually tight—in part because Rosalyn’s father, Edward, a diabetic and an alcoholic who beat her mother (the kids “would jump on him to break it up,” Rosalyn says), was often too ill to show up at his job as a sanitation worker. “We were forced to be responsible at an early age,” says Rosalyn, who was raking leaves for cash by the time she was 8. After Edward died in 1968, mother Madeline went on welfare between factory jobs, and Rosalyn and her siblings took babysitting or clothing-store sales work to make ends meet. Rosalyn, an ace typist, hoped to become an executive secretary, but after high school she wound up at Ford. “My mother taught all of us to sew,” she says, “so it was easy.”

She was fast, and made good money—as much as $1,200 a week. But for the next 20 years she longed for something that would bring her more satisfaction. “I wasn’t using my mind,” she says. Encouraged by second husband John Smith, now 50, a Ford plant executive who is the father of her daughter Jasmine, 11 (she has three children, Vester, 22, Shannon, 19, and Ashley, 15, from a previous marriage), she tried jewelry making and lingerie sales before sitting down to become a writer.

“English was my favorite subject in high school,” says Rosalyn, who passed her downtime at Ford reading Harold Robbins or Sidney Sheldon. On medical leave after a 1989 auto accident, she started writing from 8 to 10 hours a day in a makeshift office at her spacious Southfield, Mich., home. A romance novel nut (“I’ve read about 200 of them”), she decided to blend the genre’s steamy sensuality with details from her own working-class life. Knowing’s heroine, a dissatisfied auto worker with an awe-inspiring sex life, suffers from alopecia—a condition causing periodic hair loss that Rosalyn has coped with since she was 18. “I wanted women to see that you don’t have to close yourself in a shell and stop living because of it,” she says.

Having taken medical retirement from Ford, Rosalyn, who has finished a second novel, feels her living is just beginning. “It’s never too late to start over,” she says. Terry is delighted (Knowing “is a good book,” she told her sister), and Rosalyn’s former coworkers, who send John home with copies to be signed, are “real proud,” he says.

But no one, least of all Rosalyn, is really surprised. “I called my book Knowing because it’s a strong word,” she says. “And because I always knew I was going to get out of that plant.”