What I was thinking about the Pettigrew issue -- and, in fact, all of Harry's actions as a cat -- is my conviction that cats cognate on about the same level as children anywhere from ten to sixteen, depending on the intelligence and personality of the cat. The difference is, they don't have the same abstract moral structure as we do, or the same socialization. So Harry, as a cat, is able to understand what's happening, but not that the rat he killed was anything other than proper prey, and now that he's dead, no longer worth thinking much about.
As a boy, Harry is certainly going to reach a place where the cat memories begin to trouble him ethically, but for now he's got enough other healing on his plate that he's content to let his cat-brain have the ruling on that matter.
And as for Minerva... well... let's just say she's a cat animagus for a reason.
Anyhow, I'm really glad you liked it! Thanks for sharing your thoughts!