All about Cassandra Clare:
Judith Lewis, best known by her pen-name Cassandra Clare is an American author of young adult fiction. She was born in Tehran, Iran in 1973. She is best known for her bestselling series, The Mortal Instruments, which was also adapted into a movie and tv series. 
She used to write fan-fictions of Harry Potter and Lord of The Rings which were quite popular in LA, where she then resided, but deleted them shortly after the release of her first novel, City of bones.
She currently resides in Massachusetts with her husband, who has also co-written some novels with her, with three cats.
Other than what's been given, there isn't about much her as she's a very private person.