Nurmi and Arias detest one another and it's been out in the open for a long time. She wanted to create a vacancy where he sits at table, so she could fill it with Fredrica Strumpf. Apart from playing checkers, is she superstitious? What harm could a sullen and stoic Nurmi, seated for the duration, possibly do? He's not going to whisper anything in her ear! Maybe she thinks his mere presence pulls in a black cloud over her mini-trial. This is the attorney she once entreated the court be retained to defend her, the only one who knew all the ins and outs. Her objection to him really does not make sense or pass the sneer test. She is her own chief counsel now.
As for Nurmi, he has been sorely disrespected, his legal advice rejected and flouted. His own practice is languishing. I suspect there is another reason to look for the exits. No attorney wants to serve in a capital case where the verdict is the ultimate penalty. That becomes part of the record prospective clients look at. He sees the defendant rocking toward unprofessional prat falls and epic failure. He wants no part of it. He has had no cooperation, knows Arias hates him and that she has written screeds to that point. He is here on sufferance.