Just hearing about Mandy's mum made him angry. He desperately didn't want to hate the woman, because she was Mandy's mum, but it was hard to empathise. Her dad shouldn't have lied, but he chosen to give up magic for the woman he loved. Neville could respect that, at least. But Mrs. Brocklehurst had no right to make Mandy feel guilty for something she couldn't control. For who she was. It was no better than the wizards who hated Muggles for not having magic.
He squeezed her hand. She'd told him bits of this before, but never all at once where he could piece together the whole story. "What you are is the best daughter she could possibly have asked for," Neville said, proud of himself for keeping his voice even and calm. "Not everyone would keep trying the way you do."