Well, didn't she spoil to Kurokawa that she was the one showing Nanaki the picture of her cheating boyfriend? I mean, obvs. it's the right thing to do as a friend. But did she really had to show this to her when they were surrounded by so many people? This doesn't seem sensible to me. Also she probably realised that superficial-af-Nanaki didn't really like him for him, but for status. This time ought to be different.
It looks like I'm basically the only one who still likes Izumi at this point. She's manipulative oc, but what you gonna do if you're smarter than anyone else in the group trying to push things towards your advantage? The moral will obvs. be that you shouldn't do that, but I still like her character-design.