It wasn't an "anti-trans manifesto", but a thoughtful explanation of her reasons for speaking out on the sex and gender issue, where she discusses her concerns for women's rights and safety, the well-being of vulnerable children, and how important it is to be allowed to speak freely on this topic. Plenty of people on the left (and centre-left) agree with her too.
As with all her work, it was very well written, which the article you linked rightly acknowledges.