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).
Answer: To try to throw them off the scent and add suspicion to make us think maybe possibly they're the killer(s).
This answer is literally part of the question. The question mentions that this was done to make the character seem suspicious. The question was asking why, in the context of the film, can't Liv go to see Tara. Not why in a behind-the-scenes sense.
TedStixon