For me, it is not relevant for the argument if it is presented as a parody or not.

Believe me, I get the gist of your point and I understand that even if you look at it in good faith, problems arise with her writing of the house elves slavery.

However, I have a problem with the statement that just because an author implements something in their world building and does not immediately make it very obvious, in whatever way, that this is a bad bad thing, makes them a supporter of said thing. Of course we never know the true intentions of the author but just assuming they wrote it so they support it is a bit of a stretch.