Because her keys were found with her vehicle, my impression is that she was at her vehicle (not on a trail) when something happened to her.
Did her vehicle break down as she was driving, then parked on the shoulder of the highway? Or, was her van parked on a pullout near the lake? If she was parked at a pullout, maybe she went for a hike and something happened when she returned to her vehicle. The timeline of sightings will help clear that up.
Pullout parking areas at Mamit Lake
There are several along the lake.
Did her vehicle break down as she was driving, then parked on the shoulder of the highway? Or, was her van parked on a pullout near the lake? If she was parked at a pullout, maybe she went for a hike and something happened when she returned to her vehicle. The timeline of sightings will help clear that up.
Pullout parking areas at Mamit Lake
There are several along the lake.