If the camera support AF assist illumination, use it. It will light up the subject for better focus tracking.
Also, if not specified, the camera will decide on which AF points to use, which may not be what you want. Try to select a AF point for the operation and aim that AF point at the subject(model).
From the picture, it is quite apparent that the car offers better contrast compared to the model. If you can, ask the model to wear something of high contrast (e.g. black and white). It may help a little, althou the effectiveness varies.
Or, like what other mentioned in another thread, try tp light up the model with a torch or something, after focus lock then switch it off, then take the picture.
why choose white car? can the girl wear white too?
the problem is black background, white car.
that will cause the camera to meter the white car and the girl wearing black is underexposed.
use tripod and manual focus on the girl (use torchlight if you cannot see her properly, while manual focusing)
If possible also try off-camera flash (manual mode, zoom to the max) and point to the girl. Dont diffuse, as the white car will then be over-exposed.
i think u should take portrait instead of landscape... move closer to the subject and use flash... as i think ur aim is to put the white car and the gal into 1 photo, i dont think u need to include the black car on the right... distracting people might say and ur build in flash do not really have that much power to brighten the surrounding...
but still i think, u wont get good image from this kind of situation unless u r prepared with proper gears... hope im not wrong... ;p