I believe that your question is asking about the short story "Lamb to the Slaughter" by Roald Dahl. The main character's name is Mary, and she gets away with the murder of her husband. She killed her husband by hitting him in the head with a frozen leg of lamb. She then cooked the leg of lamb and fed it to the clueless detectives.
Mary is not a murdering psychopath. In fact, she is not even remotely unhappy with her husband, Patrick. She is the quintessential doting wife. She sits quietly at home waiting for Patrick to come home from work, and then she practically waits on him hand and foot.
She took his coat and hung it in the closer. Then she walked over and made the drinks, a strongish one for him, a weak one for herself; and soon she was back again in her chair with the sewing, and he in the other, opposite, holding the tall glass with both hands, rocking it so the ice cubes tinkled against the side.
For her, this was always a blissful time of day.
Unfortunately for Mary, Patrick apparently doesn't feel the same way for her anymore. Soon after arriving home from work, he makes an announcement to Mary. The reader is never told what the announcement is exactly, but the reader can be quite sure that Patrick told Mary that he is leaving her or wants a divorce.
“This is going to be a bit of a shock to you, I’m afraid,” he said. “But I’ve thought about it a good deal and I’ve decided the only thing to do is tell you right away. I hope you won’t blame me too much.”
And he told her. It didn’t take long, four or five minutes at most, and she say very still through it all, watching him with a kind of dazed horror as he went further and further away from her with each word.
“So there it is,” he added. “And I know it’s kind of a bad time to be telling you, bet there simply wasn’t any other way. Of course I’ll give you money and see you’re looked after.
A few minutes later Mary struck Patrick dead with the leg of lamb and proceeded to secure her alibi in order to get away with the crime.