The key to keeping art and artist separate is does the artist allow their beliefs to influence their art or not. There have been many writers whose later books are unreadable due to rampant misogyny or racism. Without editors to file off the rough bits, the writers' true views come to the fore. Taken as a whole, though, the Potterverse seems pretty inclusive. So, while one can have issues with the author, in this case, it doesn't seem that she allowed it to affect her writing. I can't recall any trans characters off the top of my head, so maybe she took the discretion is the better part of valor route, and didn't include characters she knew she wouldn't be able to portray fairly.