I asked Cat about it, framing it as a party she already knew I was planning for an out-of-town guest who is coming later in the summer (really out of town, since I live 100 miles away from my old hometown, where many of my old friends still live). I brought up the fact that Lynn used to be my friend, and I am not openly hostile to her, and some of the people who will be invited are very close to Lynn.
Cat's exact words: "Lynn bothers you more than me, I can deal with her in small doses, but I know she really rubs you the wrong way."
Doesn't really sound like someone she'd be over-the-moon about having at her birthday party. Plus, Cat's roommate, Becky, also really does not like Lynn (Lynn posted something inflammatory on Facebook, Becky disagreed, Lynn dogpiled her with her college friends, then defriended Becky). They have no open hostilities... but, yeah. However, Lynn's best friend, Angel, is invited, and she already told Lynn about it. Lynn wants to come. I don't think Angel realizes how hurtful it is when Lynn calls everyone who disagrees with her stupid and brainwashed, and how most of the group considers her a "small doses" person, just because Lynn never calls her stupid and brainwashed. Angel knows that Lynn can be hostile about her politics, but she says that we can all be mature adults and that Lynn won't go out of her way to start a debate. But... it still seems like more hassle than it's worth. I don't usually talk politics at parties (since I'm pretty radical), but it doesn't seem fair that Becky and I will have to chew our tongues all evening if Lynn drinks.
I already know I'm not going to invite her to the party for my out-of-town guest, because based on some of her previous behavior, there seems a high chance that she will sexually harass him, which she seems to do a lot to attractive young men when she's been drinking. I do not want to subject him to that.