Dude, no way were you being unreasonable.
If she wants to go to the shops let her take her own car. If she didnt have a car, then fair enough, you should have offered to pay for a cab.
I virtually never took my 911 on short commutes to the shops. Whats the point? its barely time to get it warmed up.
It is a bit dumb arguing about it though. But she should have respected your opinion. If you say no then you mean no.
I mean, where the hell is it going to end? Its the thin end of the wedge.
Would you have let her cart a barrel of fish around in it? or perhaps a couple of wet long haired dogs?
No way would you. You dont want your car smelling of fish and dogs. And you dont want your car being driven to the mall and parked next to an SUV.
Hope that helps.
Alex "In real life in scared of my girl friend" Counsell.