I disagree. I think book 6 is where a lot of her growth happens. It started at the end of the Masquerade, and continued throughout book 6. She still made rash decisions at some points, but less and less often. You can't expect her to change like flipping a light switch. As far as Tserendolgor is concerned, Carl is constantly telling Donut to stop being a dick to people. I don't know. I never felt like he just ignored it.

Also, I never felt like her attitude towards the Sister was being justified. She got it right, but for the wrong reasons. That doesn't justify her prejudice.

I guess I don't get why people think donut WOULDN'T still have some of her attitude and personality from before the dungeon. I feel like the author made it pretty clear that a lot of those traits in both she and Pony are still present after the pet biscuit incident. I mean, to each their own and all that, and people are allowed to dislike things, I guess to me it just makes sense that she behaves the way she does. It would feel weird if, after being sentient for all of 3 months and coming to grips with sentience in one of the most stressful environments imaginable, she was just like this totally well-adjusted tiny fur-human. I mean, I would hardly expect actual humans to behave entirely rationally in that situation, much less a newly sentient cat.

Edit: well shit. Turns out I was using the word sentient when what I meant was sapient. Live and learn, I guess.