My partner has a great theory for dealing with this kind of person, which I've dubbed malevolent benevolence. Here's how it works, every time you see/hear about these people say something nice about them. When you see her on the road? Wave and grin like she's Santa. It's worked well in my adult life, if only because it's so unexpected. Sure, she'll still mutter darkly and be a pain in the ass but she'll know for dang sure she hasn't affected you in the slightest. Ignoring her doesn't have nearly as much impact as the Ned Flanders treatment. And it gives every one else the benefit of seeing you behave in a way the exposes her lies.