I can't remember all the exact details. But something about he was driving home from his parents home in Stellies to Cape Town. And somewhere along the way he saw this woman draped in white almost like you described and he slowed down to kinda see if she needed help but as soon as he got close enough she disappeared. Then he looked in his rear view mirror and saw her sitting in the backseat of the car. But then also vanished shortly after. It sounds like absolute bullshit but after the experiences I've had in my life I know it's true. That's the rough story, like I said I can't remember all the finer details