Her 143-page long book How to Make Love to a Man became a best-seller in 1981. The book took two years for Penney to research, which included interviewing more than 200 men and reading numerous books, but her biggest challenge was writing it in a tone that would be acceptable to the mass market. Clarkson Potter gave an advance of $75,000 for the book, its largest to that time, but wanted extensive changes after Penney delivered the initial manuscript. The book was published on May 22, 1981 and had sold 130,000 copies within its first five months, and had paperback rights sold to Dell Publishing for $275,000.

Self magazine's first annual issue for National Breast Cancer Awareness Month came after an April 1991 lunch at the 21 Club, at which Penney discussed ideas for articles about breast cancer with her friend Evelyn Lauder who was then the Senior Corporate Vice President of the Estée Lauder Companies and was also a member of the board of overseers at the Memorial Sloan-Kettering Cancer Center.

Together with Evelyn Lauder, Penney established The Breast Cancer Research Foundation and formalized the pink ribbon as a symbol for breast cancer awareness as part of Self magazine's second annual Breast Cancer Awareness Month issue in 1992. Penney's inspiration to improve on the success of the magazine's first annual issue was to create a ribbon that would be placed in Estee Lauder's New York City stores. Evelyn Lauder made the commitment to have the ribbons placed on the company's cosmetics counters across the United States.

Having been employed by the magazine since 1989, Penney left Self in July 1994 to assume the position of director of new media development at Condé Nast Publications, in which she would be responsible for developing new opportunities in print and broadcast media for the firm. Less than a week later, Penney announced that she would stay at Self where she wanted to pursue the challenge of surpassing the magazine's records for advertising revenue and circulation that had been set during her tenure at the magazine.

Penney had earned a substantial amount of money from her writing, almost all of which was invested with Bernie Madoff after a good friend steered her to Madoff in the 1990s assuring her that her money would be safe. As of early 2009, she owned an artist's studio in the SoHo neighborhood of Manhattan, a cottage in West Palm Beach, Florida and what was described as a "beach shack" in Wainscott, New York, all of which she had paid for over four decades from her earnings. While she did not disclose the amount of her losses at the advice of her lawyers, Penney indicated that she still had enough money in her checking account to last a few months. Penney wrote a series of posts on The Daily Beast titled "The Bag Lady Papers" starting in December 2008 in which she chronicled her experiences and feelings in the wake of the Madoff scandal.

Penney purchased a frame house in the Flamingo Park Historic Residential District, West Palm Beach, Florida with her companion, painter Dennis Ashbaugh.