I would say that the majority of your adjectives would need to come from the beginning of the story, because Dahl is very careful to build up a precise nature of Mary's character to prepare us for the massive situational irony that occurs in the middle of the story. The adjectives I would use to describe her would therefore be loving, devoted, subordinate, serving and obsessed. This would be from the way in which she greets her husband and the high level of love that she has for him. Consider the following quote:
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.
Note the way in which the centre of Mary's existence is said to be her husband, and the way that she waits on him and does what he wants without even thinking of her own needs and wants is rather disturbing in its slavish devotion. Of course, all of these qualities makes her shift into a calculated master criminal all the more surprising.