Natalie was very well-done. (While we were watching, it was suggested that perhaps she was over-the-top, but I think that effect came from the cinematography rather than her own acting.) I am having difficulty parsing her motivation, though.
Her pushing her younger sister Chloe out of the treehouse seems like sociopathy to me (in large part because I saw that episode of The Inside -- Cat and Emma can vouch for the fact that I literally said, "What's with little girl sociopaths pushing people out of treehouses?") but Grissom says, "This girl holds me responsible for the death of Ernie Dell. I took away the only person she ever loved, so she's gonna do the same thing to me." (Sidebar: That we get everyone's silent facial reactions -- starting with Catherine -- is priceless.) This made me think of mamadeb's comment on mari4212 personal canon meme response: "sociopaths are incapable of crushes because they just don't care about anyone else.
At one point, Cat suggested that she coded a lot like someone with autism but that they should have caught it by the time of the treehouse since she would have been significantly language-delayed. However, it was pointed out that this was the late-seventies/early-eighties and with her mom dead it might well have been chalked up to poor/absent parenting. And we never hear her speak in any of the flashbacks, so we don't have any evidence that she wasn't significantly language-delayed.
Also, we get the bleach as the dad cleans up the blood (and Grissom says something like, "I wonder what it looked like to her") which makes the bleach linkage somewhat awkward. Does she come to associate it with killing rather than it triggering it directly? (And given how much prep work goes into each murder, I'm unclear as to how exactly it would function as a trigger anyhow.) We open this ep with her stumbling out of a convenience store freaking out after bleach spills, though. (And this recap mentions that when Ernie Dell's asking her about the murders she mentions "that smell.")
Back in "Lab Rats" when Hodges found the common element of bleach in all four models, Grissom said: "James Tilly Mathews. Early 19th century London. Mathews was in Bedlam hospital awaiting trial. Doctors were trying to determine his sanity. Several interviewed him. Half thought he was sane, half insane. Turns out he was perfectly normal, except when someone mentioned politics. At that point, he'd go into a rage about the little men who lived underground and used a bellows to push thoughts into his mind, as well as the minds of Parliament, and the Queen. A specific object or word triggers the urge to kill. That's a form of delusional psychosis. Rare, but it does exist." [source: tv.com]
Thus in this episode, Grissom's statement: "Female serial killers are rare enough. Delusional psychosis in women? Rarer still."
Oh, and the above-linked recap also explains that the next-door-neighbor in the bathtub was stealing his neighbor's electricity and his poor wiring job killed Trevor. So why the model? This recap says, "Catherine explains it away by speculating Natalie gave it to Trevor since he collected action figures." (Yeah, this is why I don't understand how people can watch shows like this other than in complete intent silence. Oh, and it also says, "Leaving Davis, Catherine is yammering on about Natalie definitely having killed Chloe but Grissom is deep in thought. He says he was imagining what the scene must've looked like for Natalie, high in her treehouse with her dead sister, father, and partygoers looking like miniatures far below.")
And Natalie's bit about being Ernie's "special girl" screamed sexual abuse to me, but maybe he was just the only person who cared about her after her biological father? Reading these recaps and thus getting a clearer understanding of the connection with the doll -- her username is "NotYourLittleBisqueDoll," with "little bisque doll" being a line in the ventriloquist song (btw, tv.com says "I've got a pain in my sawdust" is an actual pre-existing song. Oy.) -- I started wondering if she was re-enacting her killing of Chloe and seeking a father figure's approval in killing Sara. I'm not sure that quite works, but it's interesting. -- Oh, and Natalie reacts to Grissom's relief at her statement that she didn't kill Sara, which would argue against her being autistic, 'cause he wasn't all that obvious and she reacts immediately and strongly.
I'm also curious about Natalie's motivation in not killing Sara outright.
"Control freaks with social problems, that's my bread and butter,"
"But this chick? She had crazy eyes."
I'm sorry, "crazy eyes" makes me laugh 'cause HIMYM.
Also: Hee. (I do the dark humor thing, so sue me.)