Maybe to try to confuse the jury?I had the exact same thought! Why a psychologist?!
The next thing that went through my mind was: These are competent attorneys, familiar with the psychiatric issues in this case. They must have read the record and determined that a psychiatrist is unlikely support their anticipated defense, whether it’s about psychosis or medications or PPD. So they’re bringing in a psychologist who’ll testify more like a “mental health professional” who’s just a glorified, tangential layperson on the medical side of things.
You would know better than me, but I’m assuming it would be more difficult to find a psychiatrist who would testify that LC’s treating psychiatrist was wrong in determining she didn’t have PPD, or wrong in prescribing the medications she was given. A psychologist might be a bit more inclined to testify from a medication-skeptical, “let me tell you about PPD,” squishy sort of place.