[That does make her laugh. She wonders why on earth you'd want a car above anything else anyway. Oh... but there is one thing. She's going to ask.]
Ah... Oh. I meant to ask... ah...
Why... did you think I was his... ah... girlfriend?
[Since you know... she hadn't met you before or anything she figures there must be a reason, right? And... well... she's curious. And also very embarrassed. But more curious.]