Cassandra is a Coda warrior who was, for reasons unknown, sent to live in exile in a castle deep in the Himalayas. She holds the rank of Lady among the Coda which means she is quite a person.
She has a very sadistic and misanthropic personality. This is shown when she kills the messenger sent by the Majestrix calling her back in action. As well later when she tortures Suzy and tries to break her into obedience.
These passions of her are probably why she got exiled.
Her exile is however rather strange, since Cassandra is shown killing the IO scientist that Christine Blaze was questioning, and that Charity was only in deep cover for a few years prior to the start of Divine Right.