In a movie full of tragedy and loss, it is Padme who loses the most, which makes Leia's memories of her mother all the more poignant and sad.

After Anakin's nightmare, Padme sees that he doesn't fully trust her. As things progress I think she somehow realizes that she's losing Anakin as he becomes more concerned with power, under the auspices of saving her. Note when she says, "Is that what this about?" I wonder how things would have turned out if Anakin had listened to Padme instead of Palpatine.

The horror on Padme's face when the Jedi Temple is attacked is palpable. She fears that Anakin is inside, not knowing that what he was doing inside is even worse than she imagined, especially when you consider that he was slaughtering younglings, some of whom were not much older than the baby that Padme was carrying. Does Anakin not realize what he is doing here? How will killing younglings give him power to save Padme, especially since it's very likely that the baby she carries is force sensitive?

It only gets worse though. Knowing of Mace's attempt to kill Palpatine, Padme then realizes that her old mentor(and the man she helped become Chancellor) is actually the one responsible for the death of the democracy that she has served all her life and wathces in disgust and horror as he destroys the Republic and the people celebrate him for it. And then comes the nightmarish moment when Obi-Wan tells her the worst news imaginable. Her husband has joined the dark side. He was responsible for the attack on the Jedi Temple and even killed younglings. Her husband is helping to destroy the Republic. While she doesn't want to believe it, I think that part of her fears that this is true. And Padme, once again, goes off to do what she thinks is right, regardless of the consequences to her.

Refusing to give up on Anakin, she learns that Obi-Wan is right. The pain is so evident as she tearfully tells Anakin that he's breaking her heart. Now, realizing what he has become, she steps away from him just as Obi-Wan emerges from her ship. And Anakin chokes her with the Force, now betraying everyone he ever loved. My belief is that Obi-Wan actually saves Padme at this moment. Anakin lets her go as he can't deal with both Padme and Obi-Wan.

After the battle, Obi-Wan returns to the ship to find Padme in critical condition. His face answers her question about Anakin as she slips away into unconsciousness again.

Now, there has been some debate over whether or not a person as strong as Padme could have died simply from a broken heart. While I think that she certainly could have, I also think that she sacrificed her life to save the baby. At this moment, Padme knows what Anakin has become, and that he's even betrayed those he loves the most. She knows that if she's alive, he will find her and the baby, or at least the baby's whereabouts. But if she's dead, then the baby is "dead" with her, or safe from Anakin. And so, Padme dies, in a final effort to protect her children, and in end, save her husband.