My opinion:
I think the story is written to portray women as morally inferior, not able to control their desires and urges.
And, she's Egyptian. The OT stories were written to portray other countries and cultures as immoral and displeasing to the "true" god.
Put those two together, particularly in light of the fact that the Egyptian civilization gave women far more rights than the Mosaic Law did, and a fable like this presents the "moral" that Egyptians, particularly their women, are sexually immoral, liars, and completely wicked people.