The Marquise and the Novice by Victoria Ramstetter

In a sumptuous chateau in nineteenth century provincial France, an innocent Irish girl, fresh from convent restraints but prepared to return to take religious vows, meets a beautiful, wealthy, sophisticated older woman, a widow whose son she is to tutor. What could be more deliciously titillating than the erotic encounter of a young red-haired Kathleen Thorn, aching with repressed sexuality, and the Marquise Anneliese de Rochelle, the dark Lesbian noble-woman whose raven tresses whip wildly in the wind as she gallops off to a rendezvous in riding attire.