Knowing Flandre’s appetite for destruction, she would probably want to drive a tank or a Monster truck, but I understand that those don’t fit the common definition of "car".
I think she would want to drive a car that is exciting, so probably a very fast car like a very expansive Bugatti or something. She could also be interested to drive a robust car customized for demolition derby. In either case, what she would intent to do with said cars would definitely not follow traffic codes! I can’t imagine her car insurance monthly fees!