Car rides

Megan doesn't like car rides. She doesn't HATE them, but she doesn't like them either. She won't voluntarily jump  in the car. I don't have to lift her in but she won't go unless I put a leash on her and lead her to the door. The moment she gets in the car she starts frothing at the mouth. She doesn't whine or throw up. She lies on the backseat quietly. Maybe this isn't too big of a problem but the frothing bothers me