I truly believe we don't have female voices yet simply because that bridge hasn't been crossed yet in the grand scheme of DCS's development. There's actually a surprising amount of female military pilots, even in fighter roles, so it's a perfectly reasonable wish-list item, but also a minor detail in the big picture.
Even the male voice-overs (outside of some campaigns) in game right now aren't exactly up to par, so I wouldn't be surprised if this along with many other voice improvements will coincide with the eventual ATC revamp.
You can take one look around the forums and understand there's a lot of things more pressing on these developers plate.
PULL UP! PULL UP! OVER G! OVER G!....... OK Betty!:joystick: