but no matter how i shoot i could only get the car in focus... but not the human...
i'm not sure abt that but i believe if u direct your flash to the correct angle where your subject(the woman) gets more light than the background(the car) it should be possible.for such set up, be it built in flash or ext flash mounted on hotshoe will not get the shot you want.
why? because the car is white and much nearer to the light source compare to the person, when the car is correct exposed, the person WILL be underexposed.
and when the person is correct exposed, the car WILL be overexposed.
solution: set up the light OFF camera, aim more to the person than the car, this is how you BALANCE up the exposure.
or else shoot in daylight.