Before I pulled up your full question and saw your examples, I already had "Women" in mind. I also didn't realize that you were an editor and not a student. That being said, I thought what I was going to say would still be relevant...
In "Women," Rich illustrates a situation that, from my point of view, could only be written by a woman. There's a sense of perspective that is given in the poem from the speaker's point of view that could only be described by a woman. The second sister is the example that I think best illustrates this:
My second sister is also sewing,
at the seam over her heart which has never healed entirely,
At last, she hopes, this tightness in her chest will ease.
A relationship is present in this poem and the woman speaking is very definitely a key element in that relationship. In that sense, I think you could say that Rich's poetry is a good example of a woman's writing. I'm thinking of this in the same way that tells me that only an Afghan, or an Afghani-American, could have written The Kite Runner. There's a sense of "place" that could only come from a certain perspective. Rich demonstrates that perspective in "Women."