It's funny that you mention ptsd be ause that's exactly where my interests lie. Why would this be a more "litigated" area than other areas in psychiatry?
PTSD requires trauma and is the only disorder that requires it. Adjustment disorder requires a stressor (and generally causes long-lasting damages unless it leads to chronic depression). Trauma could be assault, MVA or rape. So it could form the basis for a personal injury case. Often you will have MDD and GAD with PTSD. However, when you have PTSD with nightmares or other symptoms specifically linked to the trauma, it clearly indicates specific causation. You don't really have that same quality representation of causation for MDD and GAD that would impress a jury. As I am specialized in BIM, I run into a lot of cases that involve PTSD and TBI (the above logic is relevant to TBI as well).
In criminal cases, PTSD could be a mitigating factor or even lead to NGRI (not guilty by reason of insanity) due to dissociation in extreme cases. Generally,, successful NGRI pleas are usually due to extreme psychosis, IDD or NCD and not for PTSD. In Texas, you have to be board-certified in forensic psychiatry for Insanity cases or have some type of CME in such work to do Insanity cases.
I see PTSD in immigration cases such as Human Trafficking, Asylum, and Violence Against Woman cases. My fellowship attending did an article about its relevance as an expert at the UN War Crimes Tribunal in the Balkans. PTSD can also be relevant to the ability of one not to recall aspects of a crime as a witness.
The issue with this researcher as an expert was that she hardly ever does clinical or expert work. She used self-report scales which may be ok in research and clinical practice that would not be acceptable in forensic work (unable to rule out malingering). You could tell that even though she knew a lot about PTSD, she did not have the skillset, expertise or experience to perform a good Independent Medical Examination.
I can see the utility in having a PTSD researcher testifying about certain issues with PTSD and having another expert do the IME (examination). If you do decide to be the examining expert, you may want to self-learn how to do one well. It would also help to treat patients and do regular IMEs.
When you become a researcher, feel free to reach out. We could co-author a paper on PTSD and Forensics.