What movie is this?

I remember watching it about six years ago... It was from the sixties or seventies and was about a woman whose boyfriend died and i called for a funeral at his mother's house out in the country. The mother turns out to be a Christian religious extremist, to point where it's become cultish. She holds the woman hostage claiming that she still has to be with her son, even though he is dead, and thus live a life without any other relationship. I remember distinctly there was one scene where the mother calls the girl into the living room to pray and the girl is wearing a red dress and the mother is furious because 'red is the devil's color'. Any ideas as to what this movie could be?