She does talk rather fast doesn't she. I don't think her knowledge of the workings and differences of the human body is at fault. What is at fault is that she thinks that the characteristics people use to infer someone's biological sex, make the biological sex.
She essentially saying the following. Biological sex is determined by several characteristics.
She points out most are changeable but acknowledges that chromosomes are unchageable.
But then essentially says that if you argue that biological sex is determined entirely by chromosomes then you are going your own way, as that is not how biological sex is determined because it has never been determined by chromosome alone, but by all these factors.
All is revealed when you make explicit the difference between determining something in the sense of inferring what it is, and in the sense of making it what it is.
As I say above, she seems to think that the characteristics that determine biological sex (in the sense of people ifrring someone's sex from these characteristics) are the characteristics that determine biological sex (in the sense of making it the sex it is).