I feel badly for the sister (did the judge say she was under subpeona?) - she didn't kill all those people, and didn't create this situation. I'm sure she loves her brother, and probably has conflicting feelings about him now.
That being said, her answers sounded coached, such as why she had never written - (loving support really can't be used against JH by the prosecution) - maybe she had strong feelings about the crime, or maybe she just doesn't like to write, but the prosecution isn't really the cause.
I understand why there was no cross, but it would have been interesting. Especially if she was asked about 'Jimmy' always being a good sport, but hitting her in the face during basketball game when she was little.
Or why she never suspected JH was mentally ill because she doesn't know anything about mental illness, but it was clear that her aunt was mentally ill - inconsistency there.
Nevertheless, I feel bad for her - I don't think she wanted to be there, IMO, JMO