Going with my feeling that she knew her abductor, we would need to know more about the people around her (her friends, co-workers, neighbors, school friends, priest, etc.), which I don't think would be an easy task since so much time has passed. Maybe in the case file it would have a listing of everyone interviewed....As for the man on the motorcycle who said he thought he saw her arguing with a male in a car and a red shoe flew out the window of said car, do we know if the motorcycle was traveling along side the car, parked on the road watching the car, travelling behind the car, etc.? If the motorcycle was travelling along with the car, the witness could have easily been off on his description as to the spot where the shoe flew out the window. And if the shoe flew out the window into a bushy, grassy spot along the road, and they did not have the correct area, it would be plausible that the shoe was never found. Searching for a body in heavy underbrush is tricky - never mind one small shoe...
Just some thoughts,
Creole