This brief but mostly accurate article about Philly-area politics and same sex marriage summarizes the issues of how we define man and woman.
The only problem, of course, is that we do define man and woman legally, and judges can do so when it comes to marriage and divorce. Just because there are more than two sexes when it comes to biological or cultural gender doesn’t mean judges can’t legally define only two. Trans people especially have had their sex defined for them – and usually not in the way they wanted.
So while her argument is valid, and imho, true, it isn’t any kind of protection against having our genders defined legally in ways we don’t like.