When I started my PPL I suffered really badly from airsickness, then I discovered 3 excellent tips...
1. Don't fly hungry. So I would be sure to eat a mars bar before every flight.
2. Keep the ball in the middle. Being out of balance triggered my airsickness really quickly.
3. Fly regularly. Flying regularly gets the body used to the motion and the brain learns what fluid motions in the inner ear are acceptable.
Hope that helps your friend and anyone else who suffers from this.