First night Carla spends at Jen's farm, there is a full moon. A night or maybe few nights, but certainly not three weeks pass, and the moon is waxing gibbous.
Carla drives her Peugeot on a rural road and the car's roof is free of ice. As she pulls up to Jen's farm, rear half of the same roof and side windows are covered in night frost while front half of the roof is glistening wet suggesting the car has just been started.