Describe Mary Maloney at the beginning of Lamb to the Slaughter. What kind of wife does she appear to be at this point?

In the beginning of Roald Dahl's "Lamb to the Slaughter," Mary Maloney is described as a stereotypical housewife. She is happily pregnant and is happy when it is approaching time for her husband to come home. All of her actions are that of a woman who is blissfully content with her station in life as a dutiful and loving wife. 

There are, however, a few descriptors that serve as forewarning that Mary may not be as stable, calm and loving as she seems. Roald Dahl uses expressions like "curiously tranquil" and noted that her eyes seem "larger, darker than before." It almost suggests that she was in a dreamlike state in the beginning of the story. Whether it was due to the pregnancy or not is impossible to say. If she was in a dreamlike state instead of actually tranquil and steady, it would explain why the shock of her husband's intent to divorce her caused her to act the way she did. It would also explain why now, suddenly awake, she is able to transform from a loving wife into a woman cleverly covering her tracks when the murder itself seemed sudden and accidental.