Demonica is the sister of Lucrezia Mongfish, and mother of Zola. Evidently she and her daughter look very much alike. There is no confirmation as to whether she is alive or dead (although Theo is not aware of her being alive).
Lucrezia Other rebel Geisterdamsel Loremistress Milvistle " " (though what exactly she did to/with/for her guest is still very unclear) and (probably) helped install mental defenses in Zola's brain in anticipation of Lucrezia's reappearance.that Demonica is/was something of a gullible naif, but Zola soon reveals that her mother kept the anti-
A footnote in Agatha H. and the Siege of Mechanicsburg says that unlike her more (in)famous sisters, Demonica quietly continued her father's work in the family's traditional lair near Minsk. Meaning you don't ever hear much about Demonica Malfeazium, and that's exactly the way she liked it.