Somehow...as "cool" as Seven is, she doesn't really strike me as a "heroine". Many might disagree--but I just don't see her that way. She seems too bitter to me, too cynical.
I see a great deal of heroism--or potential for heroism--in the more "innocent" female characters of Trek. An air of clear-cut devotion to what is good, coupled with an enthusiastic optimism for the future--is, I think, a central element to heroism in such characters as Ezri, Rand, etc.
Oh, I very much disagree. I think there's the potential for heroism in many different personality types and personally, I think that it's often more interesting when that heroism comes from someone cynical and conflicted like Seven.
I don't disagree. But the central element is heroism--regardless of its form.