Madame Velix is a Geisterdame who seems to be the person in charge at an opera house in Paris. She is evidently undercover, as she wears a blue suit rather than traditional Geisterdamen clothing, and has a pair of goggles with fake pupils for her eyes, perhaps enabling her to pass as an albino human. (Although she is yet to be seen actually wearing the goggles.) Her collar-insignia identifies her as serving the Queen of the Dawn, who is almost certainly some aspect of The Other.
She is also involved with, if not leading, a conspiracy to smuggle large amounts of miniaturized slaver-wasp hive engines into Paris, presumably to be used to enslave the entire city's population. She is working in some capacity with The King of the Silver Lands, and assists in his attempted of the Immortal Library of the Grand Architect. (Not to mention sharing more of his general hamminess than has been seen in her fellow Geisters to date.) In the process of this, she is by Larana Chroma and the hive engine which she has been lugging around is scooped up (or at least pointedly noticed) by Dimo.