I'm pretty sure Casandra became Priscilla because the organization used Priscilla's arm they took from Raki to create the three new Abyssal Beings. They were able to create them because of Priscilla's intense hatred to Youma, which has now given her the power of creation. They said that she isn't just regenerating, but creating her new limbs. And since Cassandra consumed Roxanne, Cassandra now has double of Priscilla's essence in her, allowing Priscilla to take over. Anyone agree? Or have I just become wildly lost?
Anyway, prediction time. I wonder if Claire will beat Priscilla using the emotion that conquers all, love. Or revenge, your pick. Because although Claire hates youma, she joined the organization to get revenge for Theresa, someone she loved. She loves Raki too, and Jean. And her friends... hmm. I don't think hatred of youma is the only thing that makes a Claymore stronger. I can't wait to see how the Claymores actually beat Priscilla, if they can at all.