She is, yes. But probably not in the ways that this will be used to target.

JK is TERF (trans exclusionary radical feminist; this is the term they came up with to describe themselves, before retroactively deciding it was a slur when people used it to describe them). She thinks of herself as a feminist, but what she does in practice is misogyny.

First off, she spends a LOT of time attacking other women, primarily trans women, but also any woman who dares to say they’re actually cool with trans women (so, most cis women). Very often these cis women will be accused of being secretly trans so that JK and her cult don’t ever have to stop and question the whole “Wow, we sure spend a lot of time demonizing women” part of their “feminism”.

Second, in order to justify her transphobia, she (like almost all TERFs) practices a brand of gender essentialism that runs directly counter to most modern feminist ideals. Basically, in order to create her impermeable wall between who is or is not a woman, she has to create increasingly constrained boxes around who and what women are allowed to be. Women have to have a vagina; fuck you if you’re intersex but feel more comfortable as a woman. Women have to be capable of childbirth; fuck you if you’re sterile. Women have to have periods; fuck if you’re post-menopausal. And so on.

But equally importantly, in her fucked up world women have to look and act a certain way. The Imane Khan incident recently is a perfect example of this. Khan has the audacity to be a cis woman who is good at a combat sport while also being relatively tall and having strong features. Because she doesn’t fit the perfect idealised weak submissive hourglass figure heart shaped ass anime face vision of womanhood that Rowling and her posse envision, they immediately declared that she was secretly a man, and demanded to have her well deserved victories thrown out. That is pure misogyny, plain and simple; attacking a woman for not looking and acting the way they think a woman should look and act.