Lol. How can you disagree with the creator of the character? It’s hilarious that the anon thinks they know more about Jo’s characters than Jo does. Seriously, I’m laughing right now!

I always figured that Umbridge had to be a Slytherin, and not just because ‘JKR always puts the bad guys into Slytherin’ either. She valued blood purity, she was highly ambitious, she valued power for power’s own sake, and she used ‘any means to achieve her ends’. Those are explicitly Slytherin traits (though of course those traits are shared by non-Slytherin characters as well).

I don’t understand why this fandom is convinced that Umbridge should be in Hufflepuff because loyal, because she actually shows very little in the way of loyalty. She is willing to use Cruciatus on Harry even though she knows perfectly well that Hermione is right when she says that Fudge wouldn’t want that (and Fudge would be horrified, if only because a Ministry employee using an Unforgivable on a minor is something Fudge will have a very hard time explaining away, even if that minor is someone they’ve been slandering for a year solid). She refuses to acknowledge either her muggle mother, her underachieving (in her eyes) wizard father or her Squib brother, out of sheer shame. From OOTP alone you could certainly argue that she’s a Fudge loyalist, and you could even argue in HBP that she’s a Ministry fanatic, but by the time DH came around it was pretty plain she’d be loyal to whoever gave her the most power and allowed her to wield it as she pleased.

For my money, a better example of the negative side of Hufflepuff would be both the Barty Crouches. Crouch Senior was so loyal to the Ministry, to order, and to justice he’d gladly screw his own son over without batting an eye, yet relented and violated his own principles in the face of the one thing he was even more loyal to - his wife’s pleas. Crouch Junior was in turn terrifyingly loyal to Voldemort, even breaking Imperius to send the Dark Mark into the sky. I would have been stunned if Umbridge had been revealed as Hufflepuff, but I’ll be even more stunned if the Crouches aren’t, honestly.