What gets me about HP fans is the excuses they will make for themselves, so they can convince themselves they're fans of the racist, antisemitic, badly written children's books created by TERF in a ~morally righteous way~.
"But I'm autistic and it's my special interest!" It was mine too, for the better part of two decades. I was still able to let it go.
"Harry Potter really helped me through hard times!" Yeah, there were times they were my only comfort as a bullied, abused, lonely kid. I still let them go.
"But I'm trans myself!" Friend, you are literally a fan of books created by someone who at best wants to take away your rights, at worst wants you dead, and is actively spending money towards that goal. Seriously, love yourself. And you're still hurting your fellow trans people, btw.
"I buy all my books/movies/accessories secondhand or from Etsy!" And when I see you read HP in your Gryffindor scarf, that's gonna make me feel more comfortable around you?
"Death of the author! Separate the art from the artist!" She is literally spending money to -- effectively, I might add -- take away trans women's basic human rights. Fuck you.
"I'm headcanoning/writing the characters as trans! Suck it, Rowling!" You're still creating fan content. You're no better than the people who write 100% canon-based fic.
"I'm only into the Marauders side of the fandom!" Oh, the Marauders parts of the books were written by someone else? Also, they're two immature bullies, a pathetic asskisser (who of course is fat, because 99% of Rowling's fat characters are evil or a joke), and a guy who's a metaphor for AIDS (stereotypically gay men!) who's too afraid of speaking up in a desire to fit in. How nice.
"I support trans rights but I just love HP so much!" Hey so whatever you put after "but" makes the first part of the sentence invalid. You are literally saying a franchise created by a transphobe matters more than actual trans people's safety and wellbeing.
You are still keeping the fandom alive. You are still spreading it so other people can find it. She is still viewing support of the fandom, especially monetary, as support for her and her views. You are in no way, shape, or form better than the unapologetically proud HP fans. In a lot of ways, you are actually worse.