To me , she is a pillar to the six fingers for a reason. Each of those guys have some kind of warped quirk to them like the guy Obsessed with the number 2, the "spider" demon obsessed with battle, and Creepy Glasses obsessed with watching despair. Hers might relate to younger siblings . That organization is filled with demons that are close to origins. I'm on the fence with her .
Fair enough, but it could be her interactions with Iruma become the key to her slowly redeeming herself. Teaching is bringing her a joy she never had before.
It's a wonder why Baal and them kept her alive for so long. Didn't even investigate her.
Up until the infiltration of Babylys, he had no reason to suspect she liked Iruma that much. She kept it secret and told no one. When he sent her into Babylys with Atori, he didn't want them blowing their covers like Atori did. He wanted them to be scalpels and Atori's issues pushed him to being a blunt instrument. When Atori attacked everyone, Baal saw Shiida's defending Iruma as keeping her cover intact, being a smart operative and looking for another chance to kidnap Iruma because they would be facing the might of every teacher in the school including Sullivan if they continued that line of attack. Sullivan relented when Poro interceded to bring back Atori, but if Iruma was being held captive, I suspect the gloves would have come off from Sullivan. The subtle, playful demon would have thought, to borrow from Harry Dresden, "Fuck subtle." So, as far as Baal knows, Shiida did the best play and is in a position of trust with the teachers now because of her heroics, making her an even more valuable asset.