An abandoned vehicle, without a call for a subscribed service, items left behind, makes self-harm the most plausible, IMO. Certain she didn't have another phone?
But,,, the alleged sighting seems vague, and if I recall, was by the tow truck driver. Who didn't offer a ride.
State Police procedural violation, or more.
Plow truck driver calls police to get vehicle moved so he can plow later. Knowingly or unknowingly hitting a smaller person in the dark, in all black clothing, isn't an improbable situation.
Too many options...