Adding to my previous comment - the police offered her a ride close to the top of the winding ravine section of that road. There are virtually no turn offs, residences, or businesses near there. If she received a ride to the top of the hill/mountain - why did she get out? Why was she walking? It seems to me that it would be incredibly unlikely that she got a ride from someone who ended their travel near MP 22 or even MP’s 15-22. It’s just one of the least likely spot I could imagine seeing a young woman walking alone and I’ve done a lot of backroad traveling and hitchhiking in my life.
The timing adds some dimension to this, though. Typically, I would expect this road to almost exclusively be traveled by locals but Klickitat is a big sport fishing town and Goldendale dubs itself the “Sportsman’s Paradise” (it’s a big vintage banner over the entrance of town), so there would likely be increased traffic for the holiday, campers and fishers. I imagine any local would stop for a woman on this road, knowing how desolate and rugged it is but the holiday broadens the net of potential rides substantially.