Lirael by Garth Nix (2003) Harpercollins

The second volume in the Abhorsen series.  This follows a daughter of the Clayr who barely remembers her mother and does not know who her father was.  She only wants to gain the sight of her cousins and settles for being a librarian.  She is especially good at Charter magic and incessantly curious about the Library, especially wherever she is not supposed to go.  At the same time, the daughter and son of Sabriel and her husband, the king, Touchstone must keep the kingdom safe while the parents must continuously cross the kingdom, fighting free magic and the dead.  What Lirael and the Prince learn can make all the difference.