"For goodness sake--get back out there! Laugh at everything she says--big hearty guffaws when she says something really stupid. Tell her how funny she is. Fall out of your chair in a fit of laughter. Invite her back again for some more laughs tomorrow."
This actually works! I moderate on a conservative chat board, and we do this to the liberal trolls that think they can hold their own with us.
Their heads eventually explode due to their true intolerance to other points of view, so if you're going to do this to your guest tonight, please pass out trash bags for your other guests to wear. Pretend you're at a Gallagher gathering (that guy who smashes watermelons for laughs.)
Report back. I wanna hear how it goes...