Source : Webster's Revised Unabridged Dictionary (1913)

Mediatress \Me`di*a"tress\, Mediatrix \Me`di*a*"trix\, n. [L.
   mediatrix, f. of mediator: cf. F. m['e]diatrice.]
   A female mediator.

Source : WordNet®

mediatrix
     n : a woman who is a mediator