Is a car doggy seat better than her crate or the sherpa? I assume both can be held down with a seatbelt but I haven't actually tried yet. Recommend a doggy car seat brand?
It depends on the dog. A lot of dogs travel fine in a car inside a crate. Others get disconcerted by losing their footing in a crate. Kodi is one of those. WE don't even have a "real" dog car seat for him... he rides in a donut-type dog bed, with a car-harness attached to the seat belt. Make sure you use a real car harness, not a walking harness. A car harness has a broad chest piece, often padded and fleecy, that will spread the impact in case of a sudden stop. These can mat their coat (though that's probably not a big problem with a puppy as young as yours) but the extra grooming is WELL worth the added safety.
Make sure you have paper towels some "Shamwows!" and no-rinse shampoo along for unexpected clean-up on the road.
A pile of extra towels can be useful for all kinds of "problems", from needing to re-line a bed after an unexpected "upchuck" to just drying off a puppy who has had to pee in wet dewy grass first thing in the morning.
Bring several different chew toys, Kongs or filled bones that you can rotate during the trip if she gets bored with all the confinement.
Bring a good long flexi. I'm not a fan of flexis for regular walking, but to exercise a puppy who needs to RLH, when there's no place safe off-leash, it can be a godsend. They can just go out on the end of the cord and run circles around you. (I've used this method to let Kodi blow off steam before classes at Rally trials!
If you have to go through mountains, you may find that the changes in elevation bother her ears. We found (quite by accident) that letting Kodi lick ice cubes while climbing through mountains kept him swallowing, which equalized pressure in his ears and kept him comfortable. Before we figured this out, he cried all the way through the mountains.
You might want to consider brining enough bottled water (of the same brand) or water from home that you can keep her on a consistent water source during the trip. More than a few of us have found that changes in water supply can cause poopy butts that you DON'T want to deal with on a car trip!!! Once you get to your destination, you can change her over to the local supply, where it's easier to manage any potential problems.