Question: Is there any particular reason why Marco Beltrami didn't return to score this film? I understand he has a voice-over cameo during the movie, so he was obviously involved in some capacity. But why didn't he write the music? Was it a scheduling conflict? Did the directors simply want to bring in a new composer? Etc.
Question: How does Richie know that Samantha sees visions of her dead father? (01:36:00)
Question: Why can Liv McKenzie not go to see Tara Carpenter, her co-worker/close friend after her near-murder attack? Her absence is done to draw suspicion on her, but as she is later revealed to not be the killer, the question is left unanswered in the film. (00:15:45)
Answer: It's never explained in the film, so any answer would be pure speculation. As you said, it was obviously done to draw suspicion onto her by the filmmakers, but there's any number of reasons she might not be able to, so really it's a case of picking your poison. (Perhaps she had a previous appointment she couldn't miss, perhaps she has a family matter to attend to, etc).