No, Sibri's new here. I quite like her! The thing about how not biting someone who passes through her if she hasn't bitten them at least before being unacceptable influence, even if she's specifically opened a gate for them, is pretty great. As is her self image as a teacher and how that interacts with her "can end up on Creation" loophole.
Yeah, at worst you can say is that her Charms focused too much on the Intelligent Fighter Wall of Snakes thing, and not the Slightly Satanic Cool Teacher thing. The fluff gives enough plot hooks, and a reason for a breakout on her part or her familiars, that she can easily get involved in any story vaguely resembling a sympathetic rebellion - one of her snakes shows up and starts playing advisor to a major character, or a skin of one of her students needles its way into a manipulator role. Really, I didn't see any dull entries; all the creatures are good plot hooks as well as combat monsters, and all the characters seem fairly interesting; the most boring is Kian-Ji, and that's mostly because he's a catalyst rather than a character in his own right. His role is to dine with people and conjure a bunch of their incarnated Intimacies - which hardly makes him something I wouldn't want to include, the problem is he's fundamentally a supporting role in other people's stories. He can be one for your players, and even better, one can know what he is and still seek him out - if you're overconfident, sure of your motives, or both, you can end up with a team made of the badass cousins of the Inside Out cast.