She needs to learn that the car is no big deal! Desensitization should help her with this.
Take her out to the car and get in. Sit there with her and say and do nothing. Wait her out. As soon as she calms down, even for a second, give her a treat and get out.
Practice this often, increasing the time you sit there. This could take a while until she sits calmly in the car.
Once she is good with sitting in the parked car, start the engine but don't go anywhere. Wait til she calms, treat, engine off and get out.
You get the idea - the car is boring and ordinary!
