A true slytherin wouldn't be so painfully obvious about their hatefulness. They're all about seizing and capitalizing on opportunity. Harder to do when people want nothing to do with you because you're such a horrible person.

I dunno, are slytherin transphobes? I see it more as jk wouldn't get the owl at all in the first place and she can mire in muggle misery

Or a Gryffindor who broadcasts it immediately everywhere she goes.