[yorkietalkjilly]

You want to change her attitude toward the act of getting into the car and associating it with something good instead of what she now fears should work if you are patient and persistent and willing to put in the time.

With some just-cooked and delicious-smelling boiled chicken I would wait until she is good and hungry and lure her nearer and nearer the open door car for a few days until she is desensitized to being near it to get her chicken with praise and a bite every time she will take even a half-step closer. Then return her to the house.
Then use that same method to encourage her to put her paws up on the edge of the car floor but do not try to lure her into the car yet. Just to touch it with her paws - over and over a few times and then back into the house - training done.

Eventually you should be able to slowly change her association of fear of the car to that of wanting to get her chicken and approving of the car so that she will even jump into the car to get her bites on one of the occasions she is placing her feet on the edge of the car. Love and praise when she does and try it a time or two more and then back in house - session over. Repeat it until she is jumping in for regular treats or a squeaky toy and eventually just jumping in on command.

This slow process of desensitization over time by repetitive replacing the fear association with that of happily getting choice food has worked to help fearful dogs I have dealt with. Use of regular treats will not usually overcome great fear so it usually takes a high-value treat and some of your time and patience. If she can't eat boiled chicken, find something else that she absolutely drools for, wait until she is good and hungry and lure her with that. Keep each desensitization episode very short but as frequent as at least once a day - twice or more if you can.

When she can jump in without a lure, you have probably won this one but look for it to come back occasionally if she is a very fearful dog. If it does, try repeating your original desensitization training. Good luck.