Who is Cassandra from The Killing Dance and what is their importance?

Cassandra is a werewolf. She petitioned to join Marcus' clan after learning what Richard intended to do with the pack. She befriends Anita and often serves as her bodyguard. In actuality, Cassandra is Sabin's wolf and the reason that he refrains from human blood. Cassandra eventually betrays Anita and takes her to Raina and Gabriel.