In need of a good "good-bye gift"(Must be creative)?

I have this teacher teacher that I have had for the last 3 years and all my friends want to give her a present or something for our big good-bye graduation gift! She is the gifted and talented teacher at our school so we need it to be some sort of puzzle-solving thing, something that will get her interested. One idea I had was to create some type of secret code and have her figure it out and it will lead her to a restaurant where we all have lunch and wish her good bye. That's not a very good idea though... anyway any good ideas would be great! Thanks!

Oh also she is considering taking a year off of teaching to write a book, so if you have any ideas related to that that would be great! GRACIAS!