The author is planning two novels based on the character as a teenager in high school.
Speaking about the prequels this week, Bushnell revealed: "'Carrie in high school did not follow the crowd - she led it. It was there that she began observing and commenting on the social scene."
She commented that Cyrus could be perfect for the Carrie role - played by Sarah Jessica Parker as an older woman in the HBO series and on the big screen.
Cyrus told TV Guide earlier this year: "I'd love to do a younger, cleaner version of Sex And The City."