The sting in the tail here is that J K Rowling should never have been famous. What happened was that, with the expulsion of the execrable Enid Blyton from the list of accepted childrens' authors, there was suddenly a massive gap in the market.
Once you've grown out of 'The Gruffalo' and 'The Snail and the Whale' etc, but before you're old enough for 'His Dark Materials' and 'Twilight', there is a period of some five or six years which, by the end of the last century, was a desert for enjoyable fiction.
Rowling is a person of average intelligence, who had one good idea, the time and patience to write it down, the perseverance to try to get it published and the luck to find a publisher who saw the gap in the market. So the kids lapped them up and middle-class parents everywhere sighed with relief "They're actually reading!" Because book good/screen bad, right?
Follows bestseller status, film contracts, celebrity and a platform. A platform which she could have used to write more kids' books, to develop the world she'd created, bask in her achievement. Or she could have simply ignored it. Instead she uses it to 'out' a major and beloved character ex post facto, and second-guess herself on a relationship she spent seven books building.
By now, we are beginning to get the idea that she's not altogether bright, yes? So then she puts out a singularly daft tweet in which she demonstrates either ignorance or forgetfulness of the fact that not everyone who menstruates is a woman and not every woman menstruates. Because the article she was moaning about was solely concerned with the safe and hygienic management of that function, especially for young girls (11-17 year olds are not yet women, but they menstruate, of course).
Now if an 'ordinary' person had done that, we'd have said "Dim as a Toc-H lamp" and ignored it. But JKRs celebrity status draws a rapid and virulent response. Then instead of saying, quite simply, "Oops, that didn't come out right!" or "My bad, I just read the article properly and now I see what they mean." she took it all personally and began to flounder around, justifying herself by talking about completely different issues and digging a hole for herself.
That's what happens when you make off-the-cuff comments without proper research or context.