BBM #1 - Throwing something out there, from way out in left field...is it possible that the location is significant not only to the perp(s) but to his/her/their history with MH? Then, a crime of passion by a known (if only slightly) offender would make sense, in the exact spot (or close to) where maybe a spurned advance at a party, concert, joy-ride, whatever some time prior led to the subsequent events...
I keep thinking the location matters a lot, but this would make it matter a whole lot more (and would narrow the set of people down to very few). This is vast speculation, and I suspect friends and family would have mentioned anything like this that they knew of, and as pointed out compellingly by others she had her own place, there's no known ex, etc.
But I was struck by the 2007 entry MH made that was linked here, iirc, that talked of a social situation spiraling down (my paraphrase), meeting a creepy guy, and giving up her last unicorns.
BBM #2 - "she appeared to be waiting for someone at the RV lot" I appreciate your causing me to take another look at this. Was this from something you read or just an assumption based on the time line? I've always assumed she walked with the BB players from UHall Lot to Lannigan Field/R.V. Lot, then proceeded pretty quickly to Copeley Road Bridge, but I believe the time line says 9:10-9:30 is when she was in and about Lannigan Field Parking and Copeley Road Bridge, and those are pretty short distances, so maybe she was waiting for someone specific to pick her up at the lot. But then why would she leave the lot and go to the bridge to hitchhike (unless it was for that person(s) to pick her up, but if so, how did she arrange that sans cell phone?). And did she forget her purse at the lot?
All this, MOO.