I think I figured something out.
Part 1 is Fear and Loathing, and it symbolizes the death of Marina.
Part 2 is Radioactive, it symbolizes the birth of Electra Heart.
Part 3 is The Archetypes, an introduction/explanation of the personalities of Electra Heart.
Part 4 is Primadonna, an Archetype.
Part 5 is Su-Barbie-A (said by Marina in an email), another Archetype.
So, Part 6 and 7 will probably be Teen Idle and Homewrecker, because she did a brief introduction, and now she's probably going into detail about each of the Archetypes.