If the person who was being "discussed" was a good friend of mine, I would say, 'Wow. That doesn't sound like her at all. She's actually a very nice person. Maybe she was just having a bad day. You should get to know her.' I would then change the subject to a topic that was less mean-spirited and toxic.
What do you want the panelists to weigh in on? Email your ideas to editor Tamara O'Shaughnessy at firstname.lastname@example.org.