JK is a 70's-era radical feminist who's always been a little transphobic (that was the era, everyone was) but in this decade got sucked into the feminist-lesbian-to-TERF pipeline and dug her heels in when people started calling her out for it. Ever increasing levels of escalation on both sides later she's weirdly become the most prominent transphobe in the English speaking world and throws her weight behind hate groups like the LGB alliance. She even got a shoutout from Putin for it which is kinda funny.
This is no way whatsoever justifies being mean to someone playing a video game but it's not hard to see how we got here. We live in a world where absolutely horrible people are so completely insulated from the consequences of their actions that the people who are harmed by them are pretty much powerless to do anything and have nowhere productive to direct that anger and frustration. In a less civilized time a mob would have shown up to her house with pitchforks years before it got to this point.