A note asking an author to write a sequel is not the same as a note asking the writer for permission to write your own sequel/spinoff/prequel to the author's story. Remember that. And try sending her another message. Then try sending an email to Jinn, the webmaster of this site, and ask if perhaps he has a way of contacting the author about a particular story. Every attempt should be made to contact the originator of a story before using the character/names from that story without permission.