It's less about giving money to the woman herself and more about how HP and JK Rowling are used as memetic weapons. Every release of a new property has seen a rush of transphobic actors invading trans spaces for years. Invoking the name of the author and showing solidarity in a lot of contexts is a not subtle way of showing support to the veiws expressed by the Terf ideology during a time when being trans is becoming criminalized in more places. The news isn't generally covering it well but Texas is passing laws where it is a criminal offense to misrepresent your birth sex at work or in public government spaces.

"Oh but it's just money" isn't so much the problem. It's the cover this entire conversation about ethical consumption or the lack thereof in daily life is providing to people throwing up open flags of anti-trans bigotry in public and using that as a tool to band together to attack the community and send open messages that trans people are not welcome in ways that the average cis person will dismiss as just "they like kid wizards".