From The Heart

It was a very sweet note from a student; thank you for all that you've done for me, etc. "I don't know what I would have done without you." And then the lines, "You are a detrimental piece to the puzzle that is my life. Thank you! I will miss you greatly."
Detrimental? I wonder, what is the etiquette, when receiving a thank you card, if there is an error of word choice? Or if perhaps she used this Hallmark card to finally air her grievances against me for @#!$ing up her Life Puzzle.