All is vanity - Christina Schwarz

As they reach their mid-thirties, Margaret and Letty, best friends since childhood, begin to chafe at their sense that they are not where they ought to be in life. Margaret, driven and overconfident, decides to rectify this by quitting her job and whipping out a literary tour de force. Frustrated almost immediately, Margaret turns to Letty for support. But as Letty, a stay-at-home mother of four, begins to feel pressured to make a good showing in the upper-middle-class Los Angeles society into which her husband's new job has thrust her, Margaret sees a plot unfolding that's better than anything she could make up. Desperate to finish her book, she pushes Letty to take greater and greater risks, and secretly steals her friend's stories as fast as she can live them. Hungry for acclaim, Margaret sacrifices one of the things most precious to her, until the novel's suspenseful conclusion shows her the terrible consequences of her betrayal.