Pretty sure you really arent in danger of anything legally. If anyone asks you about it, just tell them that some crazy chick bummed a ride of you and you took her to the gas station, aint your business what shes doing inside there. And I dont think this small theft is anything someone will say was coordinated from inside the car. So as long as you dont lie when asked, like saying you werent there, it shoulld be fine. Dont do favours for her again though.