You need to Capture her being hypnotized by Rinny, first.
Afterwards you need to talk to Cassie, afterwards you need to talk to Rinny, afterwards you need to leave Transylvania, afterwards you come back to Transylvania to see her and talk to her.
You dont need to Capture her but you can get a Scene that I might have missed so try it out!
Continue as planned. Good Luck Soldier!