Forensic Science Mini-Mystery I Answer

Since Lubbock died by his car with his key case in his hand, he was preparing to drive away, probably in pursuit of Thurston. If he had seen her or her parked car, he would have approached her or looked for her instead.

He was shot from the direction of the hedge. She could therefore have shot him only by moving her car out of sight and then returning to hide and wait for him. He left the inn so soon after she did, however, that there was not enough time for that. She therefore did not shoot him.