This case is tough to untangle. I think that's because at least one of her "friends" is not being "totally honest," and LE seems to be playing this close to the vest in many ways (which I can't disagree with in the absence of all of the knowledge they have). For some reason I get Twin Peaks vibes from this whole situation (smart/popular kid goes missing in small, insular, isolated town).
Some observations and questions:
1. When and where was (and what was she wearing in) the last sighting of KR that was confirmed by LE?
2. Why did KR and SS become sudden friends their senior year? The first two things that come to mind aren't rock n roll.
3. KR's mother, (on and off/ ex-?) boyfriend, and one of her best friends attended a car show in Reno (I think that's why they all went there, although not all together? perhaps I'm wrong) and she initially planned to also go with her mom, but then changed her mind. Why did KR change her mind not long (hours? day(s)?) before the party? Who changed her mind? What were the possible motivations of someone else for changing her mind (did they have something "special" lined up for her?)?
4. Where was KR and where were her friends (and what were they doing) between the time KR was recorded on video at gas station store and the next/last confirmed sighting(s) of her?
5. Why would KR's friends not clarify for days (until LE did) that she was not wearing the black sweatshirt, but instead the white & pink one? LE said they were both relevant, so it seems likely that she changed sweatshirts at some point. Why would she decide to do that (or did someone else do that?)? Blood (from a fight? ... fighting mentioned as traditional part of party(ies) there)? Vomit (if someone saw her vomit, it would be hard(er) for them to explain letting her drink more, ingest substances, letting/making her fight, not finding her a ride home, and/or leaving her unattended with strangers, etc.)?
6. Why would SS leave her young, inebriated "close friend" mostly (or completely) with "sketchy," much older strangers in the woods past midnight, with no known ride for her (other than driving her own vehicle), and assume she wouldn't drive home while intoxicated and would instead either find a ride home (from a sketchy stranger or two?) or sleep there (alone in her car amongst a bunch of sketchy strangers?) until morning?
7. Was there some "special" thing or event already awaiting KR that night, a night she previously didn't plan to be there? A fight, a challenge, a substance??