Sabriel

Description for SABRIEL by Garth Nix:

Since childhood, Sabriel has lived outside the walls of the Old Kingdom, away from the power of Free Magic, and away from the Dead who refuse to stay dead. But now her father, the Mage Abhorson, is missing, and Sabriel must cross into that world to find him.

With Mogget, whose feline form hides a powerful, perhaps malevolent spirit, and Touchstone, a young Charter Mage, Sabriel travels deep into the Old Kingdom. There she confronts an evil that threatens much more than her life - and comes face to face with her own hidden destiny. . .

This is #1 in Old Kingdom Series.