Okay so, yeah, her. She was... a hireling that was hired to deal with Miyuki's capture, who might or might not make an appearance one day, depends did she manage to escape Marcus's wrath in the end. And partially why she isn't in the epilogue is because I forgot her existence after one and a half years.
There were in a sense three plotlines running parallel to each other. The "main" aka getting rid of Malachai, the company, and the world. The attacks on the Great Houses were part of the "world" plotline so to say, it partially exists to show that the world is living and things don't only happen to the MC and his happy not so little harem.
There were some things that crossed each other in non-obvious ways at times, it was mostly a "happy coincidence" that a potentially awakening sorcerer was delivering an Egyptian ring to a lich, forgot did have the diadem there right now, but at least a ring. And no one stopped to ask why the lich wanted a new body. Without the MC, Mei would be the new body for the lich right now. Thus what would he do with the new body, outside of probably locking himself into a room with a mirror for a month or two, but that's beside the point. The lich was part of both company (the delivery, who was the customer who ordered it) and the world plotline (trigger for Alexander's awakening, and the question "why"). Two of those were seen, the delivery and awakening. The other two? Well, this isn't my first rodeo on creating something that spans multiple installations, I know that there needs to be left some threads open so you can return more easily, and give the readers moments of "ooooh it meant that!".