Of course I wrote her back -- immediately.
Her letter reminded me of a very rude thing I did at about her age. A good friend of mine moved to Australia. She sent me a card, at my classroom. I took the card out of the envelope. Threw away the envelope and took the card home. It never occurred to me that I could write her back. My grand daughter's teacher is helping her learn a skill that will let her keep in touch with friends who move.
When I tried to tell my daughter, how excited I am, she said she wished the teacher would teach her daughter to send email. I love email. I love the instant gratification. But I also remember when I was 9 I wrote to my grandfather, and I loved the surprise of getting his letters in the mail -- the unpredictability factor was part of the fun. After I joined the club at my local family restaurant (Big Boy's) I got a membership kit that included two secret decoder cards. I sent him one of the cards always remembered to put a special message in my letters in code.
Yes, I look forward to getting emails from my grand children. But letters have an emotional kick to them, that is worth teaching.