I believe she has dissociative Identity Disorder, which the first defense Psych alluded to.
I feel she created an alter ego of a blonde sexualized childlike personality. She began to become lost in this alter ego and the lines began to blur between her prime Jodi personality and her created pigtail "blondie" personality. When this confusion of persOnalities happens, it causes the patient to become paranoid and violent. Patient is not aware of the presence of an alter. When patient acts out as one personality, the other personality is typically dormant and unaware of the actions of the other. They are known to have horrible headaches which might explain her debilitating headaches as her personalities are shifting back and forth during trial to try and remtrieve memory of the events. Their alter egos are typically over sexual and steal money and engage in risk taking behavior that their prime ego would find revolting.
These people can still pass as "normal". Roseanne Barr actually has DIssociative ID and has admitted to believing she probably has 22 alter egos brought on largely by when she was a prostitute and developed personas to woo men and seperate her prime identity from the sexual abuse.
Unfortunately, many murderers on trial falsely claim a dissociative identity disorder in order to claim innocence as their prime personality wasn't aware and they were insane. This creates problems for people like Jodi who legitimately do have it and are insane.