Just jumping in here. Have not had enough time to read 10 threads on this case. Looking at the boat dock and ramp area and putting my head in that of the perp's.
The boat ramp is a great place to dump a car. 50/50 bet if it was left there or the original intent was to run it down the ramp into the water and something spooked the perp and he just left it there. I assume it was dusted and checked. Doubt an experienced perp would have left prints anyway.
It would need to be an individual who knew about the boat ramp. It's not something you would stumble across unless the perp is a stalker and drove all the roads a number of times and chanced across the boat ramp and boat dock....unless she suggested it as a meeting place.
Great egress to 544 and all the back roads in the area. Could not ask for a better place to drive a car into and dump it with a low percentage chance of being seen, and a quick escape in a second car, or quick escape on foot to 544 and anywhere else in the country.
Does not look like a place that I would want to meet someone after dark.
Are all the boats at the dock registered and membership required? Do they rent slips to someone traveling? If so, did LE check the log book to see what boats were there at the time she went missing, and after she left? Any still missing? Any police report about a stolen boats in the area?
Were ground scent dogs used at the ramp imprinted on a scent article? If not, huge chance was lost to determine if she was there or the car was dumped by others.
Lots of wooded area. Lots of lagoons. SAR worst case nightmare, short of the Rockies in the middle of winter.
Outlier theories:
1. Someone met her at the ramp in a boat with the pretext of going for an evening boat trip.
2. Interstate truck driver on 544.