Dear Mrs. Klein,
I'm sorry because you'll move... But I'm thankful for what you tough me, our discussion teacher-student which were like friend to friend and thank you that you always listened to me and gave me good advices. It was a pleasure to met you and to become more than a teacher in my life. I hope we'll still talk and you'll be forever an good example to me. You're the best english teacher from my entire life.
Yours sincerely, (numele tau)