Sarah Marshall has a great, juicy essay up at Lapham's Quarterly about how Marie Antoinette became Marie Antoinette: how, as a teenager who needed to prove her worth to the court by procreation but whose husband couldn't get it up, and whose mother wrote her letters saying she wouldn't succeed on account of her "beauty, which frankly is not very great, nor your talents nor your brilliance (you know perfectly well you have neither)", she decided that fashion was her best shot at gaining respect.
Like her timid husband, Marie Antoinette was descended from Louis XIV; unlike her timid husband, Marie Antoinette had the Sun King’s ability to use her wardrobe and charisma to project an air of compelling regality. She also, Weber suggests, may have gestured toward the kind of masculinity she could not dare approach in her actual conduct, through “phallic” wigs and scandalously androgynous riding garb. If she could not be a real dauphine, she could at least dress with kingly regalness.
Marshall defends Marie Antoinette's notorious spending as unexceptional, citing other examples from the era:
During her tenure as Louis XV’s mistress—a salaried position paying 150,000 livres a year, not counting gifts from the king himself—Madame du Barry frosted not just herself but her animals with millions of livres worth of jewels, gifting, for example, a diamond- and ruby-encrusted leash and collar to her pet spaniel, Dorine.