JK is a mixed bag. She was immediately labelled as "anti-trans" for her comments, but they weren't directly anti-trans. But they also were a bit anti-trans.
Her initial comments were mild at best. When criticised about them, she basically insinuated that transgender women shouldn't be allowed to call themselves "women" because it takes away from the suffrage of women.
Which makes complete sense in a vacuum. Women do suffer. But in modern society, transgender people suffer more than women. So her comments come across as, "suffrage is bad, but only my suffrage"
It's a sad mix though. She's standing up for feminism but in the process, she's discounting others.