Travel

I wouldn't give her anything to go sleep. What I would do is until Christmas, take her on rides with you for shorter periods of time, 0.5 hour and gradually more (maybe 1 hour) to get her used to the car. During the ride in Christmas, maybe take a break after a couple of hours of driving... I'm sure she would be fine.

Take her for a few short trips now. It could be she will be fine. We let ours travel in a cage and they can go for several hours without problems. If you can get away without medication all the better. A few treats underway might be good. 4 hours should be no problem. Make sure she is protected, has a harness on and dont let her out of the car without being on the leash. She might panic and run off. At your destination take her in on the leash, watch she doesnt escape.