I would probably describe the relationship between Steve Harmon and Kathy O'Brien as realistic and professional. Steve has been accused of a crime. O'Brien is a defense attorney, and her job is to defend her client regardless of guilt or innocence. Readers and Steve get this impression very early on when we are told that she is "all business as she talks to Steve." O'Brien might be like this with everybody; however, she might be like this with her clients out of necessity. She's not likely to win every case, so some of her clients might go to prison for a very long time. O'Brien doesn't want to emotionally invest in somebody that she might not ever see again. This is a very real possibility with Steve, because readers are given the impression that O'Brien believes that Steve is guilty.
She thinks I am guilty. I know she thinks I am guilty. I can feel it when we sit together on the bench they have assigned for us. She writes down what is being said, and what is being said about me, and she adds it all up to guilty.
"I'm not guilty," I said to her.
"You should have said 'I didn't do it,'" she said.
Regardless of why she acts this way, O'Brien is clear that she is there to do a job. Defending Steve is that job, and she does her job well. She coaches Steve through his testimony, and she is consistent with her updates on how the trial is going. Steve does try to get her to open up and be more personable, and he meets with some success. Steve does get O'Brien to talk about some of her school experiences, but it never goes beyond that. Their relationship stays firmly planted in the professional realm. I could describe it as cordial, but I would never describe it as friendly.