How does the story show that love can turn to hatred?

In the opening of Roald Dahl's short story "Lamb to the Slaughter," readers are given a view of how loving Mary Maloney is as a wife. Dahl writes the living room in which Mary is waiting as a cozy setting. It is "warm and clean, the curtains drawn, the two table lamps alight," and "fresh ice cubes" are waiting in an ice bucket because she has gotten whiskey drinks ready. She is patiently and contentedly awaiting her husband's return and has everything ready for him after a long day of work.
When Patrick arrives, Mary attends to his needs by taking his coat, making his drink, and giving it to him while he sits in his chair quietly. Dahl writes the silence of them just sitting in their chairs as a "blissful" part of Mary's day because she loves to "luxuriate in the presence of this man." Although Patrick remains distant as he unwinds from his day, Mary continues to try to attend to his needs by jumping to get him another drink or retrieve his slippers—neither of which he wants her to get for him.
It is at this point that the bliss and contentment in Mary begins to fade. Patrick tells Mary bad news, and readers can guess it is that Patrick is leaving Mary. A shadow is cast on Patrick's face to highlight the change in him.
Mary also goes through a change, as she goes from being an adoring, loving wife to a killer. At first, after Patrick's announcement, she continues on as normal and does what a loving housewife would do by getting something to cook for dinner. It is when Patrick snaps at her that he doesn't want her to make him anything that Mary breaks. Without thinking, she hits him with the leg of lamb, causing the table with the lamps to fall over and also causing Patrick to fall dead. The setting of a once "warm and clean" room is now in disarray, reflecting Mary's life. She has completed her transformation from a loving wife to someone filled with hatred.

William Congreve in his play The Mourning Bride (1697) has one of his female characters make the following statement, the last part of which has been quoted and misquoted countless times ever since.
"Heaven has no rage like love to hatred turned,
Nor hell a fury like a woman scorned."
In "Lamb to the Slaughter," the author Roald Dahl intentionally emphasizes how strongly Mary Maloney loves her husband. She dotes on him. She adores him. She admires everything about him. Then when he rejects her, she reacts with a burst of rage. Her action is all the more shocking to the reader because her feelings turn from loving to violent in minutes.
Is this credible? Congreve would probably say yes. Mary has several reasons for changing so drastically. For one thing, she is six months pregnant and her husband is walking out on her. She never would have expected that of the man she adored. For another thing, she not only realizes that Patrick does not love her, but she sees that he is not the same man she always thought he was.