Greta, the Mad Butcher(1977)

Once commited to her care, You'll be too terrified to die!.. You'll choke with fear!.. Recoil in horror from her unleashed fury!..

A young woman feigns illness in order to infiltrate a mental hospital, where she investigates the disappearance of her sister, a former patient. Meanwhile, the hospital warden and her attendants abuse and torture their charges, forcing them to star in cheap skinflicks.