OK, i was re-watching the Sith and that part made me wonder... Its when Padme ship lands and Anakin goes straight to her..This is how the dialog goes: P:Anakin, all i want is your love. A: Love won't save you Padme, only my new powers can do that. P:But with what cost?You re a good person, dont do this ....... P:Come away with me, help me raise our child, leave everything else behind while we still can. This is the part. Has Padme understood that Anakin now is a Sith? Because after her conversation with Obi-Wan she was still in denial. Now, from the part that i wrote, does she know it?
I believe she knew...always known hence her need to go to Mustafar after her talk with OW. Padmè's seemingly denial looks to me as more of an attempt to consciously deny the truth to herself and fails thus her last words in the coversation with OW: P:"I don't believe you...I can't.." OW: "Padmè, I must find him!" P: "You're going to kill him, aren't you?" OW: "He has become a very great threat." P: "I can't." In short, she does knows and her statement on Mustarfar is nothing more than an attempt to reach her husband.
She knows, but thinks that she and she alone can bring him back from it. Which is why she went, and did not tell Obi-Wan that she was going. I've seen a lot of interpretations of "Let's leave this all behind while we still can!" but I think it was pretty much literal: let's get out of here while we still can, because as soon as Obi-Wan finds out where you are, he is going to come here and try to kill you, and any other surviving Jedi will do the same. She believed that there was still good in Anakin and that she could and should try to bring that out of him. Luke proved 20 years later that she was correct. I do wonder what might have happened if Obi-Wan had not stowed away on Padme's ship and appeared while Anakin and Padme were talking. Anakin turned because he believed that it was the only way he could save Padme's life. I wonder if there would have been any other way for Padme to convince him otherwise.
Padme knew. A huge part of her just didn't want to acknowledge Skywalker's turn to the dark side. Notice her facial expression and her reaction to Obi-Wan after tells her that Anakin had turned to the dark side. You're wrong! How can you even say that? She thought she knew Anakin. But she didn't know exactly what he was going through, although he had expressed his fears to her. When she catches up with him on Mustafar, she can't believe the words that she's hearing from him. She far in denial.
P:Anakin, all i want is your love. A: Love won't save you Padme, only my new powers can do that. P:But with what cost?You re a good person, dont do this ^ That last line makes it seem as if Padme knows that Anakin's seeking out of "new powers" is leading him to the Dark Side to becoming a Sith. P:Come away with me, help me raise our child, leave everything else behind while we still can. ^ "Leave everything behind" I interpret as absolutely everything: their families/friends, Naboo, Tatooine, the Senate, Jedi Order, etc. She seems to suggest that they go away into hiding as they will be safe nowhere. Then Anakin starts on his "rule the galaxy together" power trip.
Of course the idea that they ever could have just gone into hiding, left everything behind and raised the children while forgetting that Anakin had commited genocide and murdered small children is totally ridiculous. But at this point Padme is a very desperate woman.