What I think I agree with is that women as currently understood is defined in relation to men, hence part of the whole heteronormative wotsit. Man, in contrast, is so often seen as default human that we don't really need to add this!
Think biblical Eve for starters, where Adam gets created first, and then Eve later as an afterthought.
So bound up with all this is what distinguishes woman (her sex), and how so much of how woman is defined is in relation to man.
So, what about lesbians, who are, potentially at least, not part of this structure. Hence not women!
No surprise if then the reaction is to reel lesbians back in, and try and make them part of the existing structure:
"I think that lesbians / lesbian identity can do this, but it can also mimic heterosexual relations and there are ways of being 'not woman' that don't involve being a lesbian. "
So, trying to make (or claim) that rather than being egalitarian, say, lesbians couples are just a poor copy of the heterosexual original, yin and yang, the same basic dichotomy.
Which actually does accord with much of my thinking, that with two females, you do have a different, hopefully more egalitarian structure of that relationship possible, for starters.
So I'm thinking that I agree with the statement in theory. I think the thinking outside the patriarchal, heteronormative structure is necessary, that to do that you must first posit that there is an outside. That our everyday conceptions of what is possible are so constrained by the expected male/female, yin/yang dichotomy, that woman itself is so linked up with all that that lesbian is potentially really outside of that structure, and hence not even woman.
Well, I seem to have convinced myself all over again that I do believe it, even if I won't say it much in everyday life because today it will be misunderstood (as saying you are a man, or a transman, or non-binary or whatever other umpteen gender identities are in vogue today!), or take a very long essay to explain exactly what you do mean.......................
Whether or not this has anything to do with what Monique meant when she said it is another matter. Perhaps I need to go read 'The Lesbian Body' again..............