As Cassandra has a variety of outfits, there exists just a great a variety to subdue and capture her. The tricky part is disarming her first, but she can often easily be subdued after that. If she's wearing her skirt and pantyhose, tie her in a skirt-hiking shibari and in a pose that emphasizes her legs or butt. If she's in her cleavage-exposing leotard, find a way to emphasize her chest. She's not good at escaping without her sword, so any effective material and tie will keep her secure for a good while.