From personal experience, the nausea will fade after getting a good (3 to 4 hour) nap or a good night's sleep. Once the nausea has passed (usually the next day), try to avoid day-time naps (despite the sleepiness) so that exhaustion really sets in by the evenings. This way, your friend will have a better chance of sleeping through the night, which will help him/her adjust to the new timezone.