I think her leaving on her on will can be cancelled out except for one stretch of the imagination: a friend/acquaintance picked her up from the Town Center and they dumped luggage later. I think that is highly unlikely because of how far away the luggage was dropped from last known location AND how close it was back towards her home; if you were running away or planning to disappear, you wouldn't backtrack towards home.
That luggage was ditched by someone else. Someone who likely knew the roads of that area and, for loose purposes, had reason to be back in that area (location of their home, work, etc). The chances of a random kidnapping resulting in the ditching of the luggage so close to the victim's home an hour in any direction from her last known location is slim to none.
While the stepfather seems a likely target, it is interesting how LE is quick to say he isn't a suspect or even a POI. Seen that before with another outcome, though. His vehicle being seen at the Town Center is pretty convincing, especially if it shows the opposite car door opened. Even if it doesn't, that would be great stretches on the effort of a suspect/perp to play that scene out hoping cameras didn't catch the whole thing.
I think we get answers soon in the form of video and hard evidence (i.e. if vehicle is crime scene, testimony mistake, messages, phone triangulation) that makes someone crack or leads LE to the right place.