To me this sounds very much like she just doesn't want the Grenadier.he retorts range from "at least it won't leak!" or 'no need to carry jerries'.
While you're still desperately looking for arguments, she has probably already decided that it's the wrong car. Men and women often justify their rejection in a roundabout way. But women are particularly good at it. If you then realize afterwards that the matter was already settled for "her", you look like an idiot.
Ask her straight out if she just doesn't want the car.