Dryad

Dryads are beautiful, but dangerous, nature spirits that inhabit the ancient forest of Athel Loren, and possibly others in the Old World. They typically appear as beautiful Elf or Human women, though their skin often has an inhuman green or brown sheen to it. When fighting, they turn into terrible snarling beings seemingly made of wood. They are elusive opponents, mercurial in their actions and difficult to read. Dryads have been known to sincerely compliment a foe on a particularly telling blow, only to take his head off moments later.

Source

 * Warhammer Fantasy RPG 2nd ED -- Old World Bestiary (pg. 92).