If the truck driver were not getting out of the truck, I'd crack the window and tell her I'm calling the police and to sit tight. I would not let her in my vehicle... to many whack-jobs out there now-a-days.
If the truck driver got out, that would put a twist on things. By calling the police for the girl, I'm now involved in the situation and would feel obligated to help out. My actions toward him would be determined by what he does.
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well armed lamb contesting the vote."
~ Benjamin Franklin (maybe)