I wonder if she could ride before they tried to advertise her as a rider, of if they taught her how to ride to match the image they were trying to sell (ie typical hollywood bs).
It's a commercial. It's supposed to be full of bs. So, I don't think it really matters. It was probably a real driver doing the driving anyway (as a stuntwoman), not this model - assuming she hadn't already got decent driving skills to begin with, of course.