I think that Meggy is sad because she thinks that nobody likes her or wants to talk to her, but really she's pretty and a good person so she shouldn't beat up on herself!
Swerving in and out of lanes, forgetting to turn on headlights (if it's nighttime), turning the car with too much of a radius, sudden breaking or turning, hunching over the steering wheel/having their face close to the windshield.
