Yes, you're right; that "rumor" was offered in jest. As noted in this Legal Times article by T.R. Goldman, one of the sources cited by Wonkette, "colorful anecdotes or descriptions about Miers are notoriously difficult to find." As Wonkette puts it, "Not even the president can think of much interesting to say about her... We're not even that excited about the possibility of her being gay."
But if you have any funny stories or good dirt on Harriet Miers, based on first-hand interaction with her, please email A3G!