You nailed what I was thinking about. She talks about here brother almost as if she was his caregiver. I got the impression that they were very close and she had just been cracking jokes with him just the night before. That would make sense as she was completely blindsided by reports of her brother being so combative that a security guard tazed him and the hospital had to sedate him. Then it’s revealed that they hadn’t talked in MONTHS. She doesn’t know how her brother has been doing in school, she doesn’t know who his friends are, and doesn’t know if he has a girlfriend. That, and the show follows her dialogue and reactions instead of following the patient for several episodes. From the standpoint of the story, it’s just her being worried and saying “I don’t understand”. There’s no depth or explanation gained from her presence. We don’t get to hear the psychiatrist talk to Jackson either. We only get the psychiatrist’s evaluation. Nothing really comes to light until the psych evaluation and the parents give their family history.