The road rage occurred on the road, I take it, and not "in the parking lot".
It's a he said/she said/he's dead situation until we hear from the deceased's passenger and sort the information out.
She says he hit her car. Who failed to yield right of way in traffic? Did he or she speed up and hit a horn instead of yielding to the other car (when pulling out of a driveway/yield/lane change)?
He "followed" her to a gas station. I wouldn't call that stalking. If he "hit" her car, he'd have to exchange information or else be cited with hit and run.
This may have been a simple accident that she called a road rage incident in order to, ex poste facto, justify shooting the guy.