AIO Girlfriend wants to go on a trip with her old friend who I’ve never met

Originally the trip involved 3 other people including my partner and her old friend, but several days ago it changed to be just my girlfriend and her old friend. She didn’t even tell me, I had to ask if it was just them now, and she got super mad at me for saying I wasn’t comfortable with that. I’m not being crazy right? I’ve literally never tried to stop her from doing anything ever before.