In NZ the rule for PPL is "Not or hire or reward", and while you can safely say you're not being rewarded you would have a hard time convincing anyone that you were taking a complete stranger for a ride but not being "hired" to do so. If anything went wrong (which is rare, I know), you would be wide open to a whole world of pain, starting with the insurance company.
I would say the best thing is to pay for a trial flight at the local aero club with an instructor. The raffle winner and their family would probably be more comfortable with that too.