Honestly be way better to take a picture of the vehicle plate, then she doesn't even have to make you aware of it, and the plate is in a database, unlike your face. On top of that, she can use a police procedure that exists for making vehicle stops: touch the side of your car with a bare hand, leaving prints on the finish for forensics.

Or, IDK, maybe she did all of the above

Edit: Now that I think about it, making you aware of it might actually be part of the plan. If you were going to murder her, you might just cut the date off early instead, saving her some time and a murder