Strait-Jacket (1964). A grown up farm girl who has a rabid temper is now the mother to a child. After catching her husband cheating on her, she murders him with an axe right in front of her child. Instead of being convicted of cold blooded murder she is ruled to be mentally insane and sent to an insane asylum.

20 years later, her doctor grants her freedom to stay with her daughter and get back to living a normal life, of-course with guidance and a routine check-up. Meanwhile her daughter wants to marry a good looking fellow from a wealthier family, only his parents are not in consensual agreement with the marriage. The two plan to get married regardless, but one problem hangs over both their heads: the rather unstable mother that is prone to violence and paranoia... [Editor's note: there is a lot more to this story, however I fear disclosing the rest would spoil a great and very unexpected surprise that makes this film such a classic psychological thriller].