She's definitely a "terf" but I don't think she's particularly militant in her feminism. Nor is her position particularly fringe. If I remember correctly, she Rowling came from a pretty shit background so I don't feel like it is surprising that someone with her history would have issue with the definition of "woman" being so mutable (and potentially co-opted by former men, the same kind of men who she was abused by).
These, "She just HATES trans people" takes are just so low-effort.
The issue isn't even really what JK Rowling's opinions are... she's just one person.
The issue is the way any dissenting opinion is treated.
I frankly don't give two shits one way or another about women vs trans, because I am straight, white, incredibly sexy man (and more seriously, it's a topic that's just too damned toxic to have anything to do with). What I do care about is the destruction of public discourse, and the way people are unable to accept or converse with anyone who holds a contrary opinion to them on divisive social subjects. For instance, calling Rowling a nazi terf cunt, and asking for her to be strung up.
I may or may not agree with what she thinks, but she has a right to say it without being threatened with personal violence, and without her entire life's work being cancelled by a lot of people too sensitive to have an adult conversation.