My theory I keep landing on is her killer was truck driver in the Hitch'n'post and overheard her talking to the waitress. He probably found her attractive, then overheard the little details that made her super vulnerable: asking for directions to a prison (showing she's not familiar with the area and whoever was waiting for her was immobile), hearing she seemed disconnected from parents/had no one looking for her ("who cares"), and then saw she left on foot at nighttime. I'm betting he drove the direction she went/towards the prison unit, offered her a ride, perhaps mentioned she could sleep in his truck, then took full advantage and did those unthinkable acts. That would also align with the theory why she had her underwear inside her to prevent any bleeding/dna leaving a trail while she was in transport to be dumped. Ugh, this breaks my heart typing this out. Even if it wasn't in that exact sequencing or scenario, I feel it was a truck driver who killed her.