She should use her vast wealth to counter-sue her accusers?
She has the means to end (or at very least, challenge) the glorification (and pandering) to all this gender 'mental illness' that's infecting the western world as we know it (and hopefully, nip it in the bud, whilst it's still a relatively small cult) and it wouldn't make a dent in her fortune.
Literally hire a team of the best scientists
(chances are, they'd provide such services for free anyhow) and lawyers to tackle all these (so-called) claims of false-biology. First define (with facts) the actual science between men and women....then watch her 'offended' accusers fall by the wayside (like a bunch of butthurt dominoes)
Threaten any of these accusers with facts and real science, and they'll *ALL* crumble.
Someone (anyone) needs to call out these deluded idiots, before their numbers (and supporters) gain traction. It makes sense, that since Rowling is on the receiving end of such abuse, she be the trailblazer that dares to call them out or (at least) sets the ball rolling for others? Her name (thus the publicity alone) would open up the doors for all those difficult questions and facts that others are afraid to address (pertaining to the 'trans' movement) for fear of 'isms' and 'phobias'. Instead of caving into these sick people, let's amplify their perceptions and lies on a world stage, cut to the chase and finally draw a line under this whole fact/feelings bullshit.....for everyone to see.
She could come out of this a real hero (And not just a lucky sub-par writer of vastly overrated children's books?)