It's been almost a decade since the college days, but some things that I thought about with this case...
Any idea what Lauren's major was? I was in a male-dominated major in college. I was the only female in my freshmen orientation group. I was one of very few females in all of my core classes. I spent so much time with these guys studying, drinking, BBQing, etc. They'd take care of me when I was drinking, sometimes being a little too protective. Sometimes I would feel the need to not be upfront and honest with them if I had met someone new that I was interested in (any time that I did date someone new, he'd usually get surrounded by a couple of my buddies from my first week of classes and get the "if you hurt her, we'll kick your *advertiser censored*" speech). Steady boyfriend or not (even now, that I'm practically married), I have been known to be the only female in the crowd. Sometimes, my SO doesn't feel like going out when my old gang is in town, but tells me to go on without him.
This could help tie some things together
Why she was with all males (even though she'd just met a couple that week).
Why JW stayed in to watch basketball while she went out.
Why the confrontation in the ally (she could have met JW's fraternity brothers that first week, became so close to them, and through them met JW).
The possiblility that she didn't want the guys to know where she was going next. It's entirely possible that CR saw her leave at 4:30, but as soon as she was out of his sight or as soon as he stopped watching her, she headed in a different direction.
Also, from my experience with "summer school", things get a little crazier than normal. Lots more drinking & partying (not sure if it's the weather or the smaller load of classes, even though they're crammed into a shorter time period), and you might be hanging out with a crowd that isn't your normal one, since there are so many people who leave town.
That said, I have a problem with the 3pm missing phone call--unless something was seen or heard while JW was looking for her. I tried not to schedule any of my classes or work before noon, because I am a night owl and knew that I wouldn't make it to an 8am