Is it permissible for a female student to offer symbolic gifts to her non-Muslim teachers in appreciation of their efforts, and is that considered a sin?

A woman's gift to a non-mahram (definition) man is permissible if it is free from temptation and suspicion. Similarly, a Muslim's gift to a disbeliever, and a student's gift to a teacher, as an expression of gratitude and appreciation, are permissible, provided they are free from any forbidden intent. It is important to note the difference between kindness and benevolence on one hand, and affection and close friendship on the other. There should be no affection between a Muslim and a disbeliever, nor close friendship between men and non-mahram women.