I know the common r/relationships answer is to cut off and burn the bridge immediately (in like every scenario, geez people use some creativity once in a while), but I have a slightly different viewpoint on the matter.

Now, that isn't to say what this chick did to you was okay even in the slightest bit. No way, it was an absurdly twisted and malevolent thing to do and I think anyone would agree with that. But, if you're losing sleep over this chick's well-being and you think it might make YOU feel better to let her crash on your couch until whenever she can get a ride back (asap, fuck the original plans), then honestly call her up and tell her to get her ass there. The way I see it, this girl is a stranger to you at this point. And as of right now, she's a homeless stranger. So you obviously have no obligation to take care of her by giving her a roof for a night or in any other capacity really, but if it's gonna benefit YOUR mood and mentality then go for it. Do you want to be a charitable person? That's the real question. Which can you live with yourself more: letting an ex be homeless for a few nights or doing a favor for someone who just betrayed you? You're gonna have to deal with it in the future, and don't think about what anyone else thinks of your decision, because they aren't important in the long run.

Anyways, and then when she leaves never talk to that bitch again, because damn what she did was fucked up in a totally seriously messed up way.