there isn't really a single quotable thing she said in this instance that can be pointed to as the 'smoking gun', it's more that to the people who are in an uproar about this, her statements are indicative of a history of saying things that aren't kowtowing to their narrative about reality and therefore rowling is evil.
Well, that's the point. I've followed multiple conversations on Facebook and on Twitter and nobody can tell me what was transphobic about Rowling's Tweets or her blog response.