Do we know for certain that cadaver dogs have been used on the van? Because in almost every scenario I can think of, BL drove to that site by Spread Creek to dispose of her. It just seems difficult to imagine she went alive to the place where she was found; you have to cross a large muddy wash (Spread Creek) to get to it, and there's nothing particularly photogenic or interesting about that spot that might have attracted her there. Possibly they were out on a hike and it was BL's choice, but again, why deliberately cross a wide, muddy wash to get to terrain that doesn't look any different than that on their original side? If they wanted a scenic hike with pictures for Gabby's blog, there were several other places along that road which were much prettier, with views of the mountains in the background. But if he drove to Spread Creek with Gabby's dead body in the van, it would have had to leave scent traces for the dogs, right?
Or possibly she was alive when they arrived at Spread Creek and parked the van alongside the road (red dot on map) and then whatever happened, happened. Now BL has a dead body he needs to get rid of. If it happened at the van, or if she was already dead by the time the van got to Spread Creek on the 27th, he would need to carry her across that wide-open wash to get to the spot where he wanted to put her (marked in blue on map.) There are a couple of campsites facing the wash, which makes me think that if he carried her across wrapped in a tarp or something, he must have done it at night to avoid being seen; otherwise that's a lot of wide-open space to cross carrying a suspiciously large and weird-shaped burden. But then he would have had to use a headlamp or flashlight and a light in that kind of pitch-blackness is noticeable for a long way and would be memorable to campers who saw it, so that doesn't leave him much better off. Add to that the fact that BL isn't a particularly big guy, he's 5'8 and only weighed 50lbs more than Gabby, so carrying her across such uneven terrain would be challenging (even more so if it was after dark.)
So that doesn't seem likely, but neither does the idea of the two of them hiking to the spot and her being killed there by a random accident. There's nothing to fall into or fall off of. If she crossed the Spread Creek wash alive, was it because BL had decided to coax her over there and then murder her? But why? If her death was deliberate and planned rather than a sudden snap or an accident, BL had to know that even if her body wasn't found, the DV incident in Moab would immediately point the finger at him. Plus his panicked reactions are more like someone who killed her in a fit of anger than in cold blood, IMO (everything in this post is completely MOO.) But it seems very odd that if BL just snapped and killed her, like during an argument, that it would happen in such an ideal place to leave her body -- an out-of-the-way, dull, unattractive spot where she would very likely not be found by humans and very likely would be found by bears and other animals who would dispose of her.
I can't help but feel that she died sometime between her last Snapchat on the 27th and the arrival of the van at Spread Creek later that day. I just can't figure out how BL got her across that wash unseen.