potentialities

And you suggest the sapping life of being a housewife when you *don't* really want to, and don't really like the people you're cleaning up after. She does sound (both in canon in your story) like the sort who can't stand crumbs int he microwave, so having teenage boys rampaging through (Harry does cooking, as I recall, presenting it as one of his Cinderella chores) can't be enjoyable.
I remember wondering, when I read about that. In canon, it reads as if Petunia is just as intrinsically lazy as the rest of them, but she couldn't be and be such a neatfreak.
I *know* it'd be easier for her to just do it herself.
But she isn't.
I'm wondering if she's trying to do a decent job of teaching Harry to take care of himself, in spite of teenage resentments. (Maybe she wrote off Diddykins as a dead loss on that score ages ago, or he just gets a free pas on everything. Illogical.)
It's harder to make somebody resistant do a chore than to just do it yourself--but she's got him doing it.
You can imagine Harry's resistance is, to say the least, inventive, fabulous, and maddening, too.
But apparently she's managed to find some motivation to make him do it anyway.
She's got no threats *left* to do it with, they've used all those up.
How'd she do it?
Now that's an interesting question, foranybody who's worked on motivating the slothful, and it speaks firmly to Harry's intrinsic character, but we don't see anything about that in canon, as far as I'm aware.
Is he a neat freak too?
Judging by the description of his room, probably not, although I've known people to be strange about different rooms of the house in that regard. It's possible that in Harry's world, the kitchen is sparkling and the bedroom a disaster.
But we don't see it from him. He's too busy feeling sorry for himself. (Which he certainly would, at that age, so it's in character.)
Appeals to intrinsic fairness, in that household??
Hunger?
You've done a fabulous job of showing how she and Harry both are NOT food-motivated, but that Petunia just enjoys watching consumption by her loved ones. Makes perfect sense.