I'm sorry, but you're screwed.
You know how some car photos are obviously taken indoors in a studio? They have complete control of the lighting on the car. There's 3 or 4 lights, and a rather standard position they place each one to get a standard effect. Then they tweak the individual lighting positions to suit the size and shape of the car.
I say you're screwed because even the outdoor photographs of cars are taken under somewhat controlled lighting.
If you take a photo in natural lighting, the sun is going to have to be at the perfect angle to make that car look beautiful. Also, I don't believe the background you use should have trees in the background. I mean the tree "stem/body" itself, not leaves. Leaves are cool.
And of course, if you want to get a decent shot of her car, you're going to have to clean and wax the outside for her.
sucker