I don't follow JK on twitter but apparently she's cool with trans folks but thinks biological women are women and a person's sex is their sex. She says biological women should be called women and not "people who menstrate" or "biological women" or "cis women".
https://variety.com/2020/film/news/jk-rowling-transphobic-tweets-controversy-1234627081/Maybe she says stuff worse than this but I don't think this stuff is that bad. People will disagree on this stuff, it's messy, who cares, we're working it out together as a society, disagreements will occur, everyone relax.