I'm reluctant to go too much into the nitty gritty of how this would work since it's best left ambiguous, but in broad strokes; the way I see it when he force chocked her, it wasn't just a force choke. I think he literally gripped her very being with the force...and he never let go.
Remember the context of the scene; he's highly emotional, blindingly furious even. Probably coursing with power after a day spent slaughtering everyone in his path. We've seen multiple times that even untrained force users can tap into an enormous surge of power when they're in a distressed emotional state, often without even consciously realising they're doing it and Anakin has the greatest force potential of anyone in the galaxy. With that in mind, what would his impulses be driving him towards when he reached out for Padme? Possession. She
belongs to him.
"You will not take her from me!"
So when he was dying in that lava pit, burned, mutilated, in abject agony and by all rights should be dead already, how is it that he's still alive? The image that comes to mind for me is that of a drowning man at sea. Desperate, crazed and fighting to keep their head above water, even if that means clutching at the person next to them, pushing them down so that they may stay afloat a few seconds more. This isn't a conscious thing, it's panic driven animal instinct and between Obi-Wan leaving and being locking in that suit, I think it's a fair assumption that Vader was not a thinking creature, but a ball of incandescent fear and rage and desperation without form or direction other than "stay alive".
So, with every heartbeat, he gripped a little tighter and tighter. The closer the black abyss came to swallowing him, the more he'd pull her down with him just to gain that extra inch of life. Eventually they switch places to he's getting stronger as she's getting weaker until he's pushed her down under the surface. So by the time he took his first breath with his new mask, she takes her last. All through this, his only conscious focus has been Padme. That's why his first words were of her and the source of his confusion:
"She was alive, I felt it!"
Just to reiterate: this is all metaphorical. An analogy based on how Lucas presented the scene. What is actually going on could be called a force link, a life drain, a transfusion of essence or even Padme willingly giving up her life force to save him. We don't know and it's best left that way.
What ever it was, Palpatine was a witness to the whole process. That's how he know
Anakin falling to the dark side is but one aspect of her anguish. We don't know whether she died from that anguish or not, but she certainly had it, from the moment Obi-Wan told her the truth, her denial, and racing to Anakin hoping he would dispell Obi-Wan's accusations. The truth would cut through her heart and leave her broken.
She believes there is still good in Anakin because there is still good in him. I personally like the mysteriousness of her death.
The cause of her "terminal anguish" would be irrelevant. The point is a person in that state of mind would either be raving hysterical or catatonic and they certainly wouldn't be aware of what's going on around them. If we're really entertaining the notion a person can "sad" themselves to death in just a matter of hours then there can't be any middle ground.
So again, I don't think the text, subtext or imagery supports that interpretation.
Besides, you didn't even comment on the fourth option!
Well that's because there's clearly no disputing it!
Vader choked Padmé into unconsciousness but I believe Palpatine used his Dark Side powers to drain the life force from her body after she was flown off Mustafar and taken to the Polis Massa medical facility. He knew Anakin hadn't killed her, but by manipulating events behind the scene (something he'd been good at for decades) he used her death to give his new apprentice the final push over the ledge of darkness and into what he felt was irredeemable evil. The anguish of believing he'd murdered his own wife and consequently their unborn child would break what remained of his spirit, which it did.
Until Luke came along twenty years later.
I have two basic issues with this: -
1) The mechanic of the whole thing. How did Palpatine even know she was on Mustafar? We saw in TCW that it takes two Sith, a particular alter and a lot of chanting to go after someone remotely. He was in Vader's surgical bay the whole time just standing there and grinning like a loon.
2) The thematics. Ultimately, the story of Anakin's downfall is one of hubris. Self defeat. Nobody tricked him into becoming Darth Vader, he made that choice himself and could have turned back from the path at any point. So it makes more thematic sense if he really did kill her in a selfish, jealous rage.
This seems like the Palpatine thing to do.
I rather think Palpatine is more likely to allow someone else to do themselves a mischief and take full advantage.
