Who played Mrs Fords Mother at the end of How do you Murder your wife?

The character of Mrs. Ford's mother in the movie "How Do You Murder Your Wife?" is not actually named and doesn't appear in the film. The scene you're likely referring to features Mrs. Ford (played by Terry-Thomas) and her daughter, who is played by Jennifer Billingsley.

The movie doesn't focus on Mrs. Ford's mother at all, so it's understandable to get confused about who plays her.