Wow. This was very good...a strange, different style, it worked very well. Lots of emotion, and a great look into Petunia's mind. (Though I really wanted to deck Dudley! That *&^@$*&^)
If I were to offer a constructive critisism, I would say that some of it is very vague, and non-specific in parts, to the point that I must interrupt the flow of the story to figure ut what you're referring to.
But that's only minor. Well done!