This page describes Cassandra's Battle Style in each of the games in which she appeared.
Soulcalibur II[]
Cassandra's moveset is very similar to Sophitia's. She attacks with her shield more than Sophitia and does a bit more of kicking. She is also faster.
https://www.youtube.com/watch?v=8WRQ65v72T8
Soulcalibur III[]
Cassandra's moveset is similar to her Soulcalibur II moveset with a few minor changes.
https://www.youtube.com/watch?v=C8oDmDDMWM4
Soulcalibur III: Arcade Edition[]
It's the same that Soulcalibur III.
Soulcalibur IV[]
https://www.youtube.com/watch?v=S8UKRi0Bu3w
Soulcalibur: Broken Destiny[]
Her moveset is the same as it was in Soulcalibur IV.