What is the ruling on offering Qur'ans, flowers, and thank-you notes to female teachers at a graduation ceremony before the final exams, given the students' fear that this might be a form of bribery?

There is no harm in honoring female teachers, for it is a form of returning kindness and acknowledging their merit. It is not considered a bribe because it is directed to everyone and on behalf of all students. A gift is an act of honoring, not a bribe given conditional on assistance.