defensatrix

Etymology
From.

Noun

 * 1) a female defender

Usage notes
In terms of form, this is the feminine counterpart of, while is the feminine counterpart of. However, it appears that has conventionally been used as the specifically feminine counterpart to  (when one is used) in the title Fidei Defensor/Defensatrix or Defensor/Defensatrix Fidei "Defender of the Faith".