She shouldn’t be nauseous if she doesn’t get general. Also, ask her if she is nauseous before you leave the hospital, they can give her drugs for it that usually work well. I have never had to leave the hospital while still nauseous, and have never had a friend I picked up throw up during the ride home.
She likely will still be groggy, so the drive home shouldn’t be that bad.
What surgery is it? Where are they cutting? Certain parts of the body are more painful post surgery than others. Go over bumps in the road slowly. The bumps will be painful. Drive slowly in general so you don’t have to make sudden moves with the car.
As far as the seat, if she is under 5’6” and your seats are low I recommend don’t put the seat all the way back. Even at my height of 5’6” When a seat is way back I “fall” back into the seat losing my center of gravity as I get into the seat. It is easier for me if the distance from where I actually sit is where the back of the seat naturally should be without a lot of shifting and turning. I hope that makes sense.
A pillow and thin blanket is good to have in case she wants it. She probably won’t.