Sadist art? Here's my concept for it. If we keep with the idea that she's the "Mistress of Monsters" who is in command of all the Dark Kingdom's various freaky monsters, I incorporated that into her design with her belt and hair ties being these toothy worm things wrapped around her. She has a parasol/scythe weapon, but I didn't include it here and might add it later.
I also gave her this Phantom of the Opera-like mask, which wasn't in the original description either but I thought it was a striking design feature that also gives her more of an unhinged look. In my thoughts, the mask serves a purpose as it allows her to psychically control/command the monsters in her army, and if the mask ever gets knocked off the monsters go wild and maybe even turn on her (for sexy results). It also gives her a unique weakness for the heroes to exploit. Let me know what you think of these ideas and this concept design.