My friend's son always gets carsick -- not just on long trips but almost every time he's in a car for even the shortest ride of a few minutes. He also gets violently ill on any plane, boat, ride, etc. He is nine now and still has not "outgrown" it, unfortunately.
I would say, based on his experience, that your child getting carsick once a month or so doesn't qualify as "all the time" as you characterized it. See if there is something in common every time she does get carsick: Does it happen mostly or only on trips of more than, say, 20 minutes? Ten? An hour? Does it happen on short trips around town or only on those winding roads you mentioned? Does it happen more in one car than in another, because one of your cars tends to give a bumpier ride? Try to figure out if there is a trigger here -- length of ride, condition of the road, which vehicle she's in, whether she's tired and missed a nap that day, whether she ate a specific food (dairy can be hard to digest, so maybe eating dairy before a drive is a trigger too, for instance). You'll need to really think through past car sickness incidents to try to track it.
She may need kids' Dramamine (motion sickness drug, available over the counter) for certain types of trips, once you figure out when she is likeliest to vomit. It would help if she could look out the window the whole time instead of down at toys or a screen etc. -- but she is so young you might not be able to get her to look out the window. You could try, by pointing things out to her. Looking up and out, toward a horizon, can help a lot with motion sickness.
For a smell like vomit, which is very hard to get rid of, I would honestly take the car to a professional detailer and tell them what they're getting rid of. Good detailers will have dealt with this all before and will be able to do very deep cleaning of the foam under the upholstery - the foam is holding onto the odor. It will cost you but will be worth it. It was the only way we got some intense odors out of our car.