**WARNING THIS POST WILL CONTAIN SPOILERS FROM SEASON 6 of THE CLONE WARS**
With that out of the way, I believe that Emperor Palpatine killed Padme using the Force. I know the arguments against this, Palpatine was on the other side of the galaxy, and couldn't possibly have known where Padme was, how could he have killed her?
Well if you've watched Season 6 of TCW, we see Dooku being held accountable for loose ends with respect to Sifo Dyas. Palpatine, while on Coruscant, chokes the mess out of Dooku, who is on Serenno. So from star system's away Palpatine is able to expertly subdue his Sith apprentice, with ease. Vaulting Palpatine to a new level of power that we had not realized possible before.
As I watched the episode, my mind flicked to Padme's death, she wasn't giving up... She was dying, for no good reason. Again she's having twins, and telling Obi Wan that there's still good in Anakin, which begs the question. Did she know she was being murdered? Precious moments she might not be able to convey that something fishy was going on... but she might try and hint to Obi Wan that Anakin was not the real evil in the galaxy. The fact is Palpatine may well have known Padme's location and tried to kill her before the twins were born. Maybe he wasn't able to get a clear sense on whether or not he fully succeeded. That kind of Force ability takes focus and dividing one's attention like that might not be wise from across such great distance. Not to mention the Jedi went to great lengths to hide the children, even dressing Padme up to make her look pregnant. Who's to say they didn't also use the Force to cloak the children.
Palpatine needed Padme gone, for a number of reasons. First, Padme was Anakin's last connection to the outside. Anyone who's studied abusive relationships knows that the abuser seeks to cut off ties with their victim. Palpatine demonstrates this incredibly well. If Padme lived Anakin would not be fully enslaved to the Emperor.
Second, the children posed an incredible threat to the Emperor. Skywalker children were basically the only beings in the galaxy who could unravel the Emperor's rule and bring balance to the Force. We see the Emperor's failure to end the twins would be his undoing.
Third, Padme posed not only a threat to his new servant, but also his political agenda. We see Padme block, and stand up to the Emperor's policies on multiple occasions during the Clone Wars. This type of political unrest wouldn't just stop because he declared himself Emperor, she presented a great threat to his political image. Her death was necessary for his smooth transition from Republic to Empire.
Fourth, and final reason. The guilt generated by making Vader believe that he killed Padme only further bound him to his master. Vader had now not only lost everything, but he thought he'd thrown it away. To him the dark side was something he apparently couldn't resist... after all, it had driven him to destroy the one person he was willing to fall for. Her death galvanized Vader to become even more ruthless in his pursuits... after all, what war crimes could he commit that would compare to his murdering his wife and unborn children?
So in short we know that Palpatine COULD kill her, he had multiple motives to kill her, and he lied about the circumstances of her death. The circumstantial evidence here is almost overwhelming. Too bad the Force doesn't leave behind any physical evidence in this case... Ah well... What do you think?
