The Collaborative International Dictionary of English v.0.48:

Tutrix \Tu"trix\, n. [L. See Tutor.]
   A female guardian; a tutoress. [R.] --Smollett.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

TUTRIX. A woman who is appointed to the office of a tutor.