J.K. Rowling has made it abundantly clear for the past 6 years and counting that she values attention more than money and loves it when people boycott her work over her hatred of trans people. She is not remotely subtle or covert about this. When you shower her with the former in a dubiously effective attempt to deny her the latter, you are giving her exactly what she wants and showing her that what she's doing is working and she should do it more. You are not helping trans people any more than her maid, her realtor, or her hairdresser are by taking money out of her pocket.
If her actual first priority was maximizing the amount of dollars that go to TERF activism, she'd make the donations privately and not post about it constantly, and if your actual first priority was minimizing it, you'd boycott her privately and not post about it constantly. None of the idiots posting about how evil supporting her is and how they always knew she was a bad egg and liked Percy Jackson or Animorphs or A Series of Unfortunate Events or whatever the fuck else as a kid instead because they were just sooo wise and virtuous actually care about helping people, they just want to feel morally superior to the unwashed masses for not doing something they weren't going to anyway.