Start slow.
Put treats on and in the car and let her play the "go find the cookies" game.
For several days, feed her in the car, with doors open. Do this until she is comfortable in the car eating her meals. Praise before putting her in, and after taking her out. Save a particularly special treat to give her as she is getting in the car.
After she is eating well in the car with the doors open, feed her in the car with doors shut.
Gradually work up to feeding her in the car with doors shut and motor running.
Next, put her in the car, drive down the driveway, then feed her. When she is done, drive back up the driveway, praise, treat, and etc.
It will take some time. It won't be done before Thursday, but most dogs can be desensitized if you take the time to do it.
Good luck!