Try introducing her to parked cars first. Once she's ok with that, turn on the engine, but keep it parked. Keep her at whatever distance is comfortable for her, and slowly, probably over the course of several days, work her up to being closer and closer to the parked car. The have someone slowly drive the car for a short distance, such as down the driveway or a little bit down the street. Again, start at a comfortable distance and move closer and closer. (of course, for safety reasons, you don't want her too close, but close enough to imitate what she will experience on the road. Then try having someone drive a car past you while you are on the street. At first, they should turn around before they get to you, when she starts to get nervous. Work on having the car come closer and closer until, after a few days, she allows the car to pass at a slow-ish pace. Repeat the exercise faster and faster cars. If she seems nervous, increase the distance
During all this, don't try to get her to focus on the car, at least at first. Keep her attention on you. Depending on your dog, this could mean giving her a belly rub or playing tug, or it could mean practicing some basic obedience like "sit", "lie down", "watch me", etc. If she looks at the car but doesn't flip out, praise her. But be careful not to scold her if she does get scared, then she'll think that when cars are around, even her human gets scary. You want to be her refuge. There is a popular belief that you shouldn't comfort a scared dog, but this simply isn't true. It is not possible to reinforce fear. So if she does get nervous, feel free to pet her, and show her that it's ok. Whenever a car approaches, make it a mini-party. Instead of letting her focus on the "scary car", help her focus on you: your praise, your pets, and your treats. It will likely not work the first time, but eventually she can learn that a passing car is a good thing.
Here is one good article: My Dog is Afraid of Passing Cars | Dog Training Nation
But be patient, this will take several weeks, maybe even several months.
During all this, don't try to get her to focus on the car, at least at first. Keep her attention on you. Depending on your dog, this could mean giving her a belly rub or playing tug, or it could mean practicing some basic obedience like "sit", "lie down", "watch me", etc. If she looks at the car but doesn't flip out, praise her. But be careful not to scold her if she does get scared, then she'll think that when cars are around, even her human gets scary. You want to be her refuge. There is a popular belief that you shouldn't comfort a scared dog, but this simply isn't true. It is not possible to reinforce fear. So if she does get nervous, feel free to pet her, and show her that it's ok. Whenever a car approaches, make it a mini-party. Instead of letting her focus on the "scary car", help her focus on you: your praise, your pets, and your treats. It will likely not work the first time, but eventually she can learn that a passing car is a good thing.
Here is one good article: My Dog is Afraid of Passing Cars | Dog Training Nation
But be patient, this will take several weeks, maybe even several months.