It's easy for you to participate. Simply write a letter to Isabella and send it to:
P.O. Box 6802
San Mateo, CA 94403
Address the outside envelope to me, not Isabella; that way you can be sure it will be delivered. And remember to include your return address!
Then check your own mail. I will write back as Isabella, in my very best cursive (please forgive its awkwardness), with a hand-dipped pen, and sealing the letter in wax. You are welcome to do whatever you please with the letter: share it with others, post it to your blog, etc.
I will answer any letters sent before the end of February, though depending on volume it may take me a little while to do so.