My principals resigning. what should i give her as a farewell gift?

okk so we form the first batch of our school and very recently answered our 12th boards n now we have come to know that our principal who has been nurturing us for 12 long years just like a mother is resigning tomorrow. so guys give me a suggestion as to wat to gift her. i love her a lot and want to gift her something which will always remind her of us.