What a horrifyingly true picture you give us of Dolores. To me, in the books she's even scarier than Voldemort - the sugary exterior and the relentless cruelty underneath.
And this story shows it to perfection. The way she uses Arabella, body and mind, is terrifying. And, as Magnetic_Pole said, a brilliant argument of why 'Obliviate' should be an Unforgivable.