My wife is the same way and it is usually due to her being on the phone or distracted in some way. I know what you mean and it is really hard not to lose your temper when you have money in gear that it's in jeoprady. My sister in law however has no problem driving in a straight line except she can't drive the car to save her life.
Next year I will have auto pilot before the season starts.
Sent from my thinking chair...