Was she trying to steal the car?

This morning me and my dad went to Tesco but I couldn't be bothered to go in so I stayed in the car. I left the car unlocked (stupid of me) and for some reason a woman in her early 20's opened the door and sat inside. About a second later she notices me and says "sorry I thought this was my car", then she runs off. I probably would've understood that it was a mistake but she was wearing a black sleeveless turtleneck, black jeans and with leather gloves. So it really got me thinking if she was a car thief?