a letter from a future prison blown our way II

Around three days later, a letter arrived in the mail.  Inside was the initial piece of correspondence in typed form, and the following message on a yellow post-it note:

shawna,
a prisoner recently escaped from our prison, la modelo.  all that was left in the cell was this letter and a faded blue piece of string.  we have no access to computers and are not sure how this letter was made.
regards,
alejandra whitebird-gonzález