I might be very wrong, but after reading a lot on this case and watching interviews with Darlie, I have a gut feeling that she didn't plan any of this in advance. I think something really exploded inside of her that night, some kind of devilish chemistry in her brain, some unexplainable reaction that resulted in such a tragedy. I don't think she calculated anything at all, she just let out all of her deepest darkest demons. And then at some point she must have realized what she is doing and panically started to stage the crime scene in order to avoid being accused for committing this horrible crime. I am not sure if she wanted to kill herself also, I think that not, because if she'd really plan the murders+suicide in advance, I think she would have chosen a different method both for boys and herself, one that would work for sure and was easier to execute.
Although I think she experienced some relief after the murders (because she doesn't seem sad, not even a bit), I also think that she has made herself believe that she's telling the truth. I know it sounds strange and complicated, but I think Darlie accepted lies for truth, that is why she can look you in the eye and say - I didn't do it.
I think she is mentally very very disturbed.
I agree that she didn't preplan it like a gang of bank robbers plans an underground heist.
I think she fantasized A LOT about how much better her life would be with just one or no kids. I'm sure she spent a lot of time daydreaming and visualizing having to spend a lot less time doing the mundane duties of a mother of three and having more leisure time.
I doubt she visualized the actual killing but it seems like she must have formulated a basic plan on how to kill the boys and where everyone would have to be to dramatically decrease the chances of Darin catching her in the murders, whatever she'd have to do to stage the scene and where she'd be and what she'd be doing when he came downstairs.
She had to make sure he and Drake were upstairs and both boys were sleeping soundly in the same room. She was at least smart enough to know she'd have to create a grizzly scene in order to sell her intruder ruse. I dont' think she was prepared for how much blood would come out of her boys. She certainly was not expecting one of them to not die immediately and to have to stab him a second round of times.
Most people, when they think of killing someone, think of only a few realistic methods. Guns, stabbings, poison, strangling.
She knew guns were out. Poison is too uncertain and might not work. Strangling takes way too long and she knew she couldn't strangle one while the other one ran away. She stabbed them both in a way that greatly increased the chance of almost instant death. Other than a shooting or pulling a Susan Smith, what better way could she devise with a built-in excuse to blame it on some unknown person?
We know she ideated suicide, and I'm sure she did a lot more than her one diary note detailed. Most people who ideate suicide do a lot more times then they ever tell. As weird as it may sound, I think she was all in on killing the boys but on the fence about killing herself.
Either that, or she decided to postpone serious attempts at suicide until after she knew her sons were dead....sort of a wait until the point of no return to make the decision. She underestimated how hard it would be to make the decision to kill herself and only half-assed the slash to her throat. Once she slit her own throat, she figured she's got a 50-50 chance of survival (based, again, on not realized how much she'd bleed) and at that point the reality and guilt kicked in and she figured she should die for her trangressions.
She played a lot of it off the cuff. Other than knocking the table over to create the illusion of a fight and maybe breaking the wine glass, she went about staging the scene rather frantically and spontaneously.
She knew beforehand she would have to do a few things to stage a fake intruder, but obviously she didn't put much thought into slashing the screen with her own knife or the fact that there would be no blood found outdoors....anywhere.... and that that would be the first and primary evidence against her.
Obviously she slit her throat over the sink. At first she was thinking like a housewife, not wanting to create an enormous mess by cleaning up the sink. Then she figured she'd toss a few things around and make it look worse.
She had her intruder worked up beforehand, at least in rough fashion, judging by her comments to 911 about looking around for missing items.
She really did not do any real homework on anything and did not even attempt to figure out how 911 responders, EMT's or detectives read crime scenes. Overall, like most staged murders, it was a completely half assed job.
Agreed, she felt enormous relief shortly after the act. Her behavior in the hospital was nothing like real grief and shock.
When I watch the Silly String video I see (morbid as it sounds) her doing a Victory Dance. She figured if they didn't arrest her in a day or two, she had gotten away with it. Watch her body language. The gum chewing. The big grins. The little jig. Now watch Darin's. Hands in his pockets (helpless, severly uncomfortable), the stiffness in his stance. The subtle disbelief in his face. He's so stunned he can't even bring himself to cry.
My unprofessional diagnosis is she's severely sociopathic and very potentially psychopathic. Someone else here mentioned histrionic personality disorder (certainly, based on her rape story from her dating Darin days) and certainly narcissistic personality disorder. Which all just means what you said, she's highly disturbed in ways that most people can not and will never understand.
Oh, and she's a pathological liar, which Darin HAD to have known by the time they got married.