(Sorry, I shouldn't have been such a grump!)
I think LS wanted to be in her apartment with CR...and that when things were so weird in her building, she wanted to get out of there more than she wanted to deal with the whole thing going on in the hallway outside of her apartment. She also may have realized that word might get back to JW sooner rather than later and just didn't want to deal with the drama of him showing up in the midst of everything. I know that if I were cheating on my boyfriend (or even if we were on a "break") and I arrived home with another guy only to find a bunch of friends or acquaintances of my boyfriend standing in the hallway near my apartment, I'd have hightailed it out of there super-STAT to avoid an ugly scene involving my boyfriend. Going into my apartment would have been the last thing I'd have done because I would have had visions of being trapped in there with an angry boyfriend on the other side of the door. And if there was a fight before my boyfriend even got there, I would be even more eager to leave.
Your post makes me think I've missed or forgotten part of the story, though. Who is Zoe? Was that someone who lived in LS' building?
I couldn't agree with this logic more - its exactly how I'd feel too and have witnessed other friends react similarly.