I really thought about this, because it's such a real-world possibility.
Mostly, it would depend on my relationship with her. If she were someone with whom I were close and valued the relationship, I would try to bring it up in as non-threatening a way as possible. The key word is "try" - I can easily imagine myself being too chicken, but I think I would do it. If we weren't close, which sounds to be the case, especially if she were not someone I generally respected and valued in my life, I'd make sure there was always as much distance as possible between us (and between her and my kid). If she were someone I generally considered to be mean or a loose cannon, I'd very actively manage my kid's relationship with her and try to debrief any interactions (if the kid is old enough - I can't remember how old yours are). "What did you think about what Aunty said about your cousin?" If I thought my sister would understand, I'd alert her to my intentions.
The other part is that I would carefully consider what I heard. We don't often get to hear uncensored what others think of us, and sometimes this can be really valuable information. If it were specific and news to you, like "JJ never shares with the younger kids," I'd try to observe my kid with her comment in mind, even if I never wanted to speak to the woman again. But if it were just something like "JJ's such a snot" when your kid happened to be tired and hungry, then I'd ignore it.
Last edited by Letitia; 02-10-2017 at 07:31 AM.