The Velvet Vampire (1971)

During a Los Angeles gallery opening, Lee and Susan Ritter, a thrill-seeking married couple, encounter the enigmatic Diane LeFanu, a raven-haired seductress of an indeterminate age. Diane has invited them to her desert hideaway for the weekend, promising all the sun Susan can handle. However, neither of them knows that their elegant hostess is harbouring a deadly secret. As vivid erotic hallucinations rob the couple of their sleep and otherworldly desire puts loyalties to the test, Lee begins to succumb to Diane's sinful allure. Now, Susan is suspicious. Is there more to Diane than meets the eye? Could she be a day-walking vampire with a thirst for love and blood?