In "Lamb to the Slaughter", what does the reader know about Mary's character?

In this excellent and darkly humorous short story, Mary
Maloney is without a doubt the most interesting character. This story is most frequently
taught at college because it is as an excellent example of the use of irony, and what is
absolutely key to this is how Dahl builds up his picture of Mary as a loving wife.
Consider how she is first introduced:

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Now and again she would glance up at the clock,
but without anxiety, merely to please herself with the thought that each minute gone by
made it nearer the time when he could come. There was a slow smiling air about her, and
about everything she
did.

Note too how her actions
are stereotypical of a loving wife: she greets her husband with a kiss, takes his coat,
makes him a drink. Note how Dahl continues to develop this image of her as a loving,
perfect wife:

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She loved to luxuriate in the presence of this
man, and to feel - almost as a sunbather feels the sun - that warm male glow that came
out of him to her when they were alone together. She loved him for the way he sat
loosely in a chair, for the way he came in a door, or moved slowly across the room with
long strides.

This is almost
an obsessed kind of love but it serves to set the stage for the situational irony of
what is to come. When Patrick Maloney tells her that he is leaving him, she strikes him
on the head with a leg of lamb and then shrewdly engineers the removal of the murder
weapon and thus all evidence of her crime. Such an act is unexpected and at variance
with the image of her that we are led to believe at the beginning of the story, and
perhaps suggests the darker message of the story - that love and hate are not so
strictly separated after all and that a thin dividing line is all that separates them.
Watch out, husbands!