a) The video has been removed from the OP. But I remember her passing a truck or something in the video. If I remember incorrectly, then my entire opinion goes out the window, and she shouldn't have been in the left lane.
b) The left lane is commonly called the passing lane in many states. Some states have laws saying not to be in the left lane unless passing (I think PA is one). But really, its just about courteous driving. If you aren't actively passing people, and traffic is light, stay to the right. It helps traffic quality, because it's a common expectation of other drivers.
But again, I stand by my opinion. If she is passing someone, then she is more than welcome to the left lane. After passing, it's best to get over. But I understand the hesitation to get over if you have someone driving aggressively behind you, as you don't know what they are going to do (ie, try to pass you on the right). So to me, in that case, its best to stay where you are, and let them make their pass (and in this case, swerve into a ditch).
Edit: Found