The liberated single woman is unable to either control her sexual urges or find a suitable partner, and therefore must turn to her dog for satisfaction.
I work with the son-in-law of the lady whose co-worker was at this party.
She comes in the front door and looks for her dog, which the boyfriend has downstairs to get the birthday girl to come downstairs.
An item of interest is an article which appeared in The Guardian a few months after this legend splashed onto the Internet in 1994.