Never received a thank you for a gift, now asked to give another gift

by Amy
( Colorado, USA)

We gave our friend's daughter money for a school trip she took several years ago. We never received any acknowledgment or thank you for the money. We have now been invited to the daughter's graduation and party. I have a "rule" that if we don't receive a thank you for a gift, we no longer give that person any more gifts. Am I being too harsh? I was brought up by my parents to write thank you notes for any gift I was given. The graduation party is this Sunday. What should we do? I'm pretty adamant that she not receive any more gifts from us.

Thank you.