Saying you "don't believe" in transgenderism is dehumanizing trans people, who go through countless obstacles and bigotry in order to live their lives. You may think that's tolerant, but you are still saying you don't believe transgenderism, and therefore trans people, don't exist. You're dehumanizing them, and that kind of dehumanization, no matter how small, feeds into the discrimination, abuse, and mistreatment trans people go through, whether you like it or not. And when it comes to one of the most popular and iconic authors of all time, with a massive global platform, if she complains about the inclusive term of "people who menstruate", then that's dehumanizing millions of trans people, and will contribute to the bigotry trans people face. So yeah, she is saying something wrong, whether she realizes it or not, because her transphobic language and behavior, even a simple tweet, will put trans people blood on her hands.