The Collaborative International Dictionary of English v.0.48:

Authoress \Au"thor*ess\, n.
   A female author. --Glover.
   [1913 Webster]

   Note: The word is not very much used, author being commonly
         applied to a female writer as well as to a male.
         [1913 Webster]

WordNet (r) 3.0 (2006):

authoress
    n 1: a woman author