Ooof. Yeah that sucks, especially since it's tomorrow. It's very hard to watch people do things they will probably regret and not be able to save them from themselves. It isn't weird that you feel stressed and upset about this. I almost had to get into it like this with a friend a year ago but we stopped speaking for other reasons related to her periodic meltdowns (mental health issues, it's just kind of a thing with her now and then so we take a break). She's well over 50 and had discovered trans activists / the cult and thought it would be the answer to everything when it would actually, for her, just be another way to try to run away from her past history of trauma (assault, rape, etc.). I was dreading having to think about trying to stop her. No idea if she went through with anything and am afraid to find out, frankly, because hearing her talk about it like it would help her broke my heart. She's vulnerable enough to go all-in with a cult like this one. Which is ironic because otherwise she has one of the best bullshit detectors of anyone I know. And while she's a sweet person, she's also narcissistic and prone to rages and verbal abuse if cornered, so if I expressed concern about it she'd probably lash out at me. It wouldn't go well, most likely.

Your friend is so close to the action date that it'd be hard to have an influence. Hopefully she'll resume talking to you down the road but don't be surprised if she goes into her shell for a while; these decisions are so bound up with mental health, insecurity, etc. that people can be really protective when challenged about something so personal. I'd just let it lie if I were you. Maybe, if it feels appropriate at some point soon, tell her you hope she's doing okay, let her know you are around and still her friend and your door is open if she wants to talk. You'll probably have to let her come to you and decide how she wants to interact or what she wants to talk about.

You aren't required to talk about this subject with her to be her friend. And that might be a path you can both take together until things become more settled.