Everything! It really is quite sickening the way that Mary Maloney panders to her husbands every whim. Just consider the first paragraph of the story and see how it presents her as a wife who is completely devoted to her husband:
The room was warm and clean, the curtains drawn, the two table lamps alight--hers and the one by the empty chair opposite. On the sideboard behind her, two tall glassess, soda water, whisky. Fresh ice cubes in the Thermos bucket.
Mary Maloney was waiting for her husband to come home from work.
Note how everything is completely ready for her husband's arrival. She has clearly worked hard to do this, and we can infer from her attitude towards her husband that she does this every single day for him as well. I know it was just Valentine's Day yesterday, but please: this is rather exaggerated. Of course, you need to be aware of what Dahl is doing through this. He is clearly setting up her character as a devoted wife, which makes the situational irony of what happens later in the story all the more acute.