hermaphrodite (sp?), born with both genitals. I'm pretty sure it's a hoax
edit- she is married to christopher guest though, who is a very effeminate man (i thought he was gay til i heard they were married, maybe Guffman was just too convincing), it makes sense to me that a female dominant hermy might be drawn to that.
If I still had access to my old genetics notes, I could tell you the proper name for what she has. She is not a hermaphrodite, and XYY is not the problem that she has. But sexually she is abnormal, and used as an example of a condition that escapes me at the moment.