There was a lot that Dr. DeMarte testified to that could be analyzed by a third party without speaking with the defendant. The MMPI raw scores are objective, but the interpretation and diagnosis of BPD require professional judgment. One of the reasons that DSM-5 is moving to more of an a la carte approach rather than the specific categories that have been used in the past is that people suffering from "named" mental disorders still present a broad range of symptoms and behaviors. You can see that it makes more sense and might be more useful to employ descriptors rather than lump everyone into a big bucket.
I'd look for the new witness to hammer home the message that there is evidence of trauma and that Dr. DeMarte's bias prevented her from seeing it, deciding instead on a personality disorder. If he's good at what he does he'll probably make a decent argument, especially because there's a lot of overlap between PTSD and BPD, and there are a lot of moving parts to any diagnosis. Ultimately, I don't think it matters. Believe it or not, it was Dr. Samuels who explained it best. He said something to the effect of "This couldn't have been premeditated, and if it was then it's very unlikely that Jodi would suffer from dissociative amnesia".
All the psychologists in the world can't make a difference in this case if the jury understands what "reasonable doubt" means. You can dismiss the gun theft as a coincidence. You can even ignore the similarities between the gun that was stolen and the gun that was used in killing Travis. I suppose it's even possible that Travis would be silly enough to keep a gun and not have any ammunition. You start to falter when DB mentioned that her destination was Mesa and ALV mentioned the same thing (even though she claimed she misspoke). When you add in the gas cans and the lies that Jodi told, as well as the odd fact that her cell phone died and recovered in exactly the places it needed to so that her diversion to AZ was hidden, reasonable doubt about premeditation dissolves completely. The icing on the cake is Jodi's history of lying and the ridiculous story she concocted to explain TA's anger and how she managed to outrun him and still had time to retrieve, aim and fire a gun.
If JM is smart, and we know he is, he'll spend about 30 seconds on the psychological testimony in closing arguments, and his main point will be "who cares?".