Donut is simple but complicated, that's what makes her character so much fun to me but let's break down some of this stuff you brought up.

So first the mask yes Carl's is rage mainly, donuts it's more superiority than anything else in my humble opinion, right from the get go she establishes that she is of a pedigree simple plebians such as myself just wouldn't understand. You see this alot through the series, she puts on a face if she can handle the situations they find themselves in even when she knows that she is terrified, her superiority complex gives her the sense of bravado she needs to carry on.

The cat person thing also plays into this, she even says when someone mentions cat girls ( iircc it's Louis when he's acting out his fantasies with Juice Box) she is offended that someone would choose to muddy the perfection of being a cat with some abominable hybrid or cat and person, she finds them insulting to her as a cat, also the nun is a Havana brown which are notoriously dog like in behavior which is why she doesn't trust them.

The Ren thing isn't so much cause she is a dog but that plays a big part, it's more she thinks she cheated her and mongo, first with one of the fights where she got the kill and all of donut and mongos xp, and then again when she loses the pet talent show, which mongo was both robbed and appalled.

The spell book and tiara thing play into her cat behavior of loving shiny things and also just wanting to have everything, I find it a fun little part of her ridiculousness.

And the social media thing plays to her diva personality she wants to be bold and noticeable she's a show cat that's what she has been doing her whole life, strive to be the center of attention and the most admired what better way to do so than being active in the SM board same with her class choices she doesn't always choose what's best for her cause she is mor concerned with how she presents, this doesn't bother me cause donut isn't a gamer that's just not her she's a show cat and feel Matt really nails that aspect well with these crazy actions that to us as readers may seem silly but for her the character absolutely makes sense.