Note: For all known map points of nameds in The Library (for "thulelibrary.txt" map files), see this quest entry.
Head Librarian Matilda spawns in the back of the library's top floor. Her PHs are the "a dutiful librarian" mobs.
She hits for a max ~8,000 and spawns health-based adds in what appear to be waves of 2-3 at a time. Adds hit for a max ~6,000 and are mezzable (they despawn after five minutes of being up).