Here’s an idea I had recently: We actually see Palpatine transfer Padme’s life energy into Vader, and this is what kills Padme.
This is an idea I floated a few years back. I saw ROTS again a week or so ago and it makes more sense now than it did them. How else does Sid Idios know she is dead? Similarly I thought that Anakin subdued by Vader is keeping Padme from passing onto the next life so she can appear as a ghost to Leia in the mode of Curse of the Cat People.