1940 / 1950 movie scene

I am looking for the name of a movie but I only remember 1 scene. The scene is a mother taking her daughter to commit her... The daughter says I will just tell them I am not crazy. The mother says all crazy people say that... When they arrive the daughter speaks up first and says I have brought my mother... The mother says I am not crazy, she is... Then proceeds to go crazy and they take her away...