Angel Above and the Devil Below (1975)

Cast: Starlyn Simone, Rene Bond, Maria Arnold, Linda York, Robert Bedford, Chesley Noone, Trickey Nicky, Nimrod Sappho, Robbie Roberson

Randy, a gorgeous, but precocious teenage girl, lies in bed reading an erotic book while listening to her young mother get screwed in the room next door. Randy stimulates her fresh tight pussy and falls into a trance that invokes the devil who appears before announcing his takeover of her lust.
Transformed into a raving nympho, she fucks everything that crosses her vision. Her mother, frightened by her change, invokes the help of a priest to exorcise the demon and even he ends up with his head between Randy’s legs.
Hollywood has The Exorcist, porn has Angel Above and the Devil Below.