Lady Brett Ashley is the only major female character in the novel. On one level she is important because she is beautiful and alluring (she is likened to the mythical Circe) and the men in the novel all are in love with her. This causes tensions, such as between Jake and Cohn.
Brett loves Jake, but it is a doomed love. She needs sex, and Jake has been left impotent due to a war wound from World War II. As she tells him, their love is hopeless because she knows she would cheat on him. Overall, she finds love painful: "I think it’s hell on earth," she says to Jake.
Despite being defined by her importance to men, Brett nevertheless has depths of character. She is a strikingly new woman, a radical departure from the Victorian angel of the home or the mannered Edwardian woman. She has broken entirely away from the ideals of the pure woman that constrained past generations of female. She has short hair, dresses androgynously, has multiple lovers, smokes, drinks heavily, and does whatever she wants. None of this is condemned, and she is in no way framed as a "fallen" woman. In fact, she is widely admired by the men for her self-possession and autonomy.
Like Jake, Brett is sympathetic as a wounded figure, an emblem of a Lost Generation that has come unmoored from the traditions, values, and beliefs of the past that once gave people identity and purpose. Like Jake, her attraction to the young bullfighter Romero comes, at least in part, from her recognition that he still is anchored in an old-fashioned world of tradition and morality that she and her peers have lost.
In general, however, the women in the novel, such as the prostitute, Georgette, are there as accessories to men and to fulfill male needs. Hemingway was not unsympathetic to women, however, and we have to keep in mind that the story is told through Jake's eyes and reflects his attitudes.
Many literary critics consider Hemingway's work to be misogynistic, as female characters often appear primarily as obstacles to male self-realization. Women in his work are portrayed mainly in relation to male characters, having a subordinate role in the plot as objects of desire or obstacles rather than being powerful and independent characters.
The main female character in the novel is Lady Brett Ashley. She was based on a real person, Lady Duff Twysden, an aristocratic Englishwoman who was known for her beauty. She was part of the expatriate community in Paris and many of the men in that community were attracted to her. She was a socialite known for her ability to party hard, as it were, including having affairs with several men and drinking excessively. In these details, Hemingway's portrait of her is realistic. She is portrayed as part of a lost generation, having little purpose in life beyond pursuit of pleasure. She is blamed for disrupting male friendship.
Georgette is a prostitute who is not fully realized as a character. She is portrayed as acquisitive and lacking wit and intelligence and does not really havr many distinctive features beyond being less appealing than Brett.
Frances Clyne is Cohn’s girlfriend and another stock Hemingway female character. Originally, she was pretty and Cohn's attraction to her was based on that, but in the novel, she has grown older and began to lose her looks and is seen mainly as manipulative and clinging.
Generally, women in the novel are valued only for their youthful sexual attractiveness and ignored or denigrated if they are not young and pretty. If they are attractive, though, they serve as a negative disruptive force in male society.
Hemingway is often considered by feminists to be a misogynistic writer. While I think this label might be a bit severe at times, in this novel Hemingway portrays his few female characters as predators in one way or another. First of all, there is Georgette the prostitute, who Jake eats with out of boredom. She is determined to get the best meal possible in Paris for her time. There is Frances Clyne, Robert Cohn's woman, who first wants to control Robert and then insults him terribly when Robert breaks up with her. The only complex female character in the novel is Brett, or Lady Ashley, whose behavior is more male than female. She prefers the company of men, prefers to be called "Brett" rather than "Lady Ashley," and wears her hair "brushed back like a boy's." Most of all, Brett's sexual behavior is might be considered more like that of a "playboy" rather than a lady, as she has a series of sexual relationships with men she does not love. Brett, who is sexually attractive yet "unfeminine" in so many ways, is the only woman who is treated sympathetically in the novel.