This issue is covered by law (Tarasoff) and in this case given what we know so far, it does not rise to the level of "Duty to Warn" on the part of the doctor. If the police had wanted to they could have committed Holmes for psych evaluation on their own authority. But they didn't. "Doctor-patient privilege" is the same as lawyer-client privilege and the requirements for violating that privilege are specific and strict. They didn't happen here.
This is going to trial. Her insurance company will make the decision to settle or defend.
I suspect they'll try to get settlements, but they might not defend if the can prove fraud on her part.
Given the fact this guy was already acting out by purchasing various components for infernal devices, if he mentioned any of that to her and she did nothing she is in some series and hugh trouble!