This is what Padme' wanted to believe. Until the very end, she held out hope that he would listen to her and follow her to wherever she would go. As she watched the Temple burn, she wanted to believe that Anakin was ok and that he was not involved in what was happening there. When Obi-Wan confronted her with what he saw on the security hologram, she did not want to believe him, saying you're wrong...he couldn't. When she confronted Anakin on Mustafar, she could not believe what she heard coming from his mouth. It was at this point that she knew that he had changed, that he really had committed the atrocities she feared

This is part of a recent blog by padmeskywalker77

http://blogs.starwars.com/padme-skywalker77/5/comments

This brought me back to a idea I had while watching ROTS the other day. It is really more of a certain point of view type disscussion and I am not arguing padmeskywalker77's point. It was an excellent blog dealing with a specific subject.
My thoughts address something else. Did Padme go to Mustafar thinking Obi-wan was wrong about Anakin? I personally think the scene after she lands is the key. She pauses and leans her head against her hand nervously. Her heart wanted to find something else on Mustafar but her mind had already accepted what Obi-wan had said Anakin had become. She had been aware for while there was something wrong as did Obi-wan but had brushed it aside.
Anyone who has had that sinking feeling before they confront the inevitable knows what Padme was going through at that moment. The answers we seek are there all along we just have to take off the blinders to see them.