Re: Star Trek III - The [Speculation Begins] (Spoilers)
But in all the Star Trek series aside from one notable exception I cannot remember one series regular human women who was a captain or first officer or even command officer. Just Janeway and I might give you Yar (although technically she wasn't from Earth but was sort of human).
Major Kira Nerys.
And for non-regulars:
Captain Rachel Garrett.
And that's my opinion.