I'm a little younger than a lot of posters here (23), so maybe I can help with my perspective on a few things. I did see some speculation about "kickback" and the friend who worked at the hotel getting money (hence the kickback), but usually this just refers to a more casual, smaller party (you're just "kicking back" with friends). Which is also why the party for the most part seems pretty chill and not super crowded.
A lot of my friends' parents were also really chill about these more illicit activities. One friend's dad actually got a fake ID for her and another friend's mom express mailed her her fake when she left it at home on her way back to school. So it isn't particularly suspicious or unbelievable to me that KJ's friends called her mom when she was missing. Most people I know would have been more willing to call a chill parent than to call 911 or alert the hotel staff who might then call 911 because they wouldn't want to deal with the police. I also haven't seen anywhere that they actually drove the car away, so if they looked in the most obvious places and then went out to the car to wait/see if she had already gone out there that doesn't seem nearly as egregious to me as it apparently does to some people.
With the new videos released yesterday showing her still partying and enjoying herself after the original live video, I just don't see how the nefarious rape/sexual assault/murder claims people are making about the original live video jive. Even if the security video at 3:20am wasn't her drunk but instead traumatized from assault, the new videos indicate any assault would have occurred at least an hour after the original live video.
I'm leaning toward tragic accident.