She used the imagery of the pig and goat to show how they were animals in her sight and not very attractive. The devil being very handsome and all in gold really shows how vain she is and her focus on looks. The story also started out with once upon a time like a fairy tale showing how it was for kids. The devil is a metaphor for an evil husband who is maybe abusive or just ingores her or takes her for granted. He is eating her which could be shown as corrupting her and making her become like him swallowing all that was her own. Hyperbole is also used in saying that "He climbed up the staircase, twenty steps at a time." The slime that came out of the devil can also be a metaphor for him being abusive and evil in general.
The intedned audience for Tetiyette and the Devil is probably young girls. The stories were generally told at funerals so anyone at the funeral would also be the audience, giving a good lesson for those present. It was a creative way to get the message through to the kids while still keeping them interested. The older men were the ones to generally tell the stories but this time it was a younger girl. This is why the story was to teach the younger girls which she had just been not too long ago some good advice.