Answer:
A good friend.
Explanation:
The letter is from a student, so we can most likely rule out the student‘s parents. If the student went to the barbecue last year, they most likely will be invited again, so we can rule out someone not going to the barbecue. If the letter was from somebody in Jenny’s family, why can’t they tell her face to face? Don‘t they live together? The most sensible answer is a good friend.
