It's always good when somebody gives an unsympathetic character a third dimension, and this is very lovely writing into the bargain. Favorite line:

It must be The Change, she thinks, although it seems too soon. She has never thought of herself as middle-aged; Dudley is barely seventeen. But what other reason can there be for this tightness of breath, the pounding of her heart, the way hot and cold shivers chase each other up and down her skin?

She scrubs at her eyes and is horrified to discover tears.

And I like how Harry is barely mentioned, but the whole arc of the story is haunted by what we know that you don't say.