How could that have gone worse? Narcissa can't force herself to change as much as Draco can't change himself, and she has nowhere to go at such short notice. Maybe she will move out? The Manor has no happy memories for her and now it is desecrated by the attack and her sons' decision to live with a man ( which I wholly condone and encourage ;)) ANd hexing the lord of the Manor is beneath Narcissa - she would not do that.

Draco calling her Mummy felt false, tbh. He is a grown-up - Mum would have suited the conversation better. "Mummy" felt condescending, mocking even.