The thing that really gets me about this one is how hard it is to apply Occam's Razor. You can get wild with any theories on any case, but usually, the simplest explanation contains the truth. Here? Something wild had to have happened. I don't believe it was SA because I don't think he could have taken her off-site, happened to be in the trailer for a phone call with Jodi at exactly 5:30, gone back off-site and happened to have been back in time to take another phone call from Jodi and have a bonfire with Brendan later. There's just not enough time for all that moving around and it's quite complicated. In order for him to have done that, he would have had to held her somewhere and killed her later. Possible. Unlikely and unsubstantiated by any evidence, but there is an entire 4 days worth of evidence missing, so this is why I would say I'm at #3 on the poll.
For someone else on the compound to have done it, they would have had to have seen her and decided right then to commit a crime, then have the frame of mind to quickly figure out how to frame SA for it. Again, possible, but given the low IQs and poor impulse control, could they have really pulled it off? Especially with the police inadvertently helping them.
Then it's not a huge leap for us to say, well, she's probably told people she's been to the Averys before. If someone outside the compound was stalking her (ex bf, roommate, character we haven't met, or even a total stranger), they could have sort of planned it out, but still would have had to have acted last minute and known the property and comings and goings of other family members. How did no one on that property see or hear absolutely nothing? I can see them not seeing the RAV being up there, but not one of all those people heard screams? Saw a fire down at the quarry? Heard a gunshot? Nothing?
Not to mention other scenarios such as The German or maybe none of the above.
There's really no evidence for anything! I can't figure out which is the most likely scenario. I am thinking the simplest scenario for Colburn finding the vehicle early is that he was on the property and found it. I can't imagine LE set it up so much that they saw her and killed her or found her dead and purposefully framed SA. But who knows? Maybe they did. Makes as much sense as anything, I guess! There are just so many layers and so many people with motive to hurt SA who is not a savory character to begin with, and TH I am afraid has gotten lost in it all, which makes me sad.