There are rumors (and rumors only) that a drug dazed, scratched up woman was found in a ditch beside Sugar Factory Road, which is north of Hardin and not close to Interstate 90, just after sunup on January 1, 2020. LE has not confirmed or denied these rumors, to my knowledge. Even if there is substance to it, she was found at least seven hours before the van left Selena at the rest stop.
I believe the reports that the other female in the van got back in it, and left with it. My guess is that SHE is the person who called to have someone drive out to the rest stop and get Selena. "She" knew Selena's family and would be likely to know someone that had the mother's cell phone number. Selena's relatives are the source of the rumor that the other female had fled to the western part of the state in the company of her own mother. I have no way of judging the validity of that.
The area is rolling grassland. The hills are fairly high, but not steep. There are the beds of intermittent streams, which are called "washouts". The most common term for a low area between higher areas is "coulee". When I first came to southern Montana 52 years ago, I would call one a "gully" and people would look at me and ask: "Where are you from?" When I traveled into the northwestern part of the state, I could still get away with saying "gully". The basic ecology is abundant wild gramma grass and prairie sage holding a very thin layer of topsoil over a deep layer of pure clay. The ground doesn't erode much, but in winter it will freeze down to about 6 to 7 feet deep. This has been a mild winter so far so it's probably less right now, but it's still frozen. This particular area is called "greasy grass country". The gramma grass (which is the "bent grass" preferred for the roughs of golf courses) takes on a particularly slick texture that makes for excellent cattle pasture but is not particularly pleasant to walk on. There is abundant wildlife, of all sizes. They are prairie animals, so they are either hibernating, or moving at night and bedding down in daylight. My guess is that nighttime would be perfect for a heat detector flyover because it would be easier to identify animal readings.
My opinion is that Selena followed a washout southeastward away from the rest stop, because it was the easiest terrain to walk on. If she followed it all the way, she would have emerged on Old Hardin Road in one to one and a half hours. More likely, she veered eastward out of the washout and across greasy grass to Fly Creek Road, which is paved. Unless some news breaks of finding a trace of her journey out there is the washout of grasslands, my opinion is that she got picked up on Fly Creek Road, a short time after the van departed the rest stop she had left behind.
All of this is my opinion only. IMO