But she's not another Ash. Ash is a hero, and he's not a bad person. He doesn't do things to the Deadites that they don't deserve. This girl murdered a kitty. It's not the same. The fact that she doesn't accept blame or even feel all that guilty--she recognizes how she is to blame, but even when she confesses to the boyfriend, she never appears actually to regret what she did (aside for the fact that it got her cursed--she only regrets that she suffers, not that she made the old lady suffer). It's not as endearing as Ash, nor as rousing. There's also the part where Ash triumphs that makes it easier to get behind him...

As for the kid, generally speaking, things done to kids are usually more horrifying for the fact that it's harder to imagine they deserve it than adults. Sure, kids are bastards, but they have nothing on adults, and adults do bad things with impunity and intent when kids are much more experimental in their bad behavior. It doesn't have to ruin the movie or anything, but it sets a certain tone. It's like how they went there with the kid in Aliens vs Predator: Requiem. It takes you aback in a way that is somewhat difficult to recover from.