I'm not sure; depends upon how smooth the ride is in your Class C. Given that you are looking at air travel between two major cities which would allow for a direct flight (i.e. no plane changes required), I would seriously consider the air travel instead. Even accounting for arriving early at the airport and waiting on baggage on the other end, you are looking at 6 hours or less door to door. If you think she will be able to get quality rest in the Class C, then that would be fine but not if she is basically going to be drifting in and out sleep the whole time.