Well, except I don't think they are using him to say she was legally insane. I have a feeling they are going to use him to explain her behavior and why she lied. They don't seem to e disputing the fact that she lied....two things from his website jumped out at me and that was bipolar (remember how little she slept according to her phone activity) and "psychosexual" under fields he has investigated.
Now what reason they would give for adding him at this late date, I don't know.
Not only are they not disputing it, remember how flabbergasted we were at the last hearing when Jose was seemingly presenting the state's case for them in exposing all of Casey's lies? In light of that, wondering if he has something up his sleeve now with this forensic psychiatrist as a witness.