I watched this about 20 years ago but I think it was from the 70’s. A group of young woman staying in a house & there’s an landlady or warden. I think at one point they accidentally killed her & covered it up.
The old woman came back and killed the young women one by one. I remember villa like house, a swimming pool and at the end all the killed women came for the last victim together with the old lady. It was the first movie that kept me awake at night.