Identify this movie (horror movie)

OK, so I saw it on a Saturday afternoon waaaayyy back in my youth - which was the late 70s, so the movie itself is either mid-to-late 1960s, or early 1970s. (Another clue that it was made during that time period - all the women in it had shoulder-length, straight hair a la Marcia Brady.)

The movie might have been dubbed into english. I recall vaguely that it was one of those flicks where lip-movements didn’t quite match up with the spoken words.

Anyway, the only scene I can absolutely recall was the finale. A young couple (man & woman) are taken to a Medeival-ish torture chambers in the bowels of some gothic estate. They are both strapped to a weird rack-like torture device (standing up, not lying down though) that stretches their bodies to painful lengths.

What was truly odd was that the device was cranked by a pale-faced zombie woman stepping on a mill-wheel. The zombie woman was manacled to the wall just above the wheel, which turned as she plodded along, and her feet hit the blades on the wheel. (Imagine a wooden stair-master machine - as zombie chick kept stepping forward, her feet landed on the blades of the mill-wheel, which kept it spinning, and subsequently cranked the rack.) I know this is must be confusing to read, but I simply don’t know how to describe it better.

Anyway, the hapless hero & heroine are writhing in agony as their limbs get stretched further & further. They call out to the zombie woman (she is obviously someone they know), and beg her for help. Zombie chick reaches out to a nearby candle and knocks it over - starting a fire that burns the rack (allowing hero & heroine to escape) and quickly engulfs the room and estate. The hero & heroine escape, but not before looking back and seeing the zombie-chick still staring off into space and plodding away on the wheel, oblivious to the spreading fire.

If anyone can actually identify this movie, I waill be incredibly surprised. But I’ll throw it out there anyway.

Mill of the Stone Women?

My horror movie freak of a husband says it sounds a lot like Seven Women for Satan.

1976, French, castle with a torture dungeon…?