I don’t think there is info that any of them dropped out, but it’s very common - especially in sororities - for girls to stop being active in the sorority in their late 3rd/4th years.
I am curious if the sororities come into play or something around Greek life - maybe it doesn’t at all, but girls can go through hell when they pledge which can stir up a lot of anger/hatred/animosity.
I was surprised to learn that K and M weren’t in the same sorority. Normally best friends would pledge the same sorority. As there are theories that K may have been specifically targeted, it’s another item that separates her from everyone else.
I tend to think this an Occam’s razor situation and we will find that a stalker type scenario is at play, particularly after seeings SGs interview. But I could also see a scenario where a girl had a very bad experience with a sorority such as not getting a bid or being emotionally abused as a pledge (potentially Alpha Phi) and had an older, protective brother that decided to get even. It’s an out there theory, but not implausible…