Halve the lesson's duration. Even less if that's what it takes to avoid the ill feeling prior to vomiting.
Fly only when it's dead smooth, so early morning. Also only when there's a clear horizon.
If it's nerves about the arrival & landing then on each flight do a couple of circuits before departing for the training area.
Keep the cabin cool and with the fresh air vents open.
If it seems to be stress from the lesson then reduce the learning curve gradient ie introduce new skills & complications later & more slowly.