"The only thing I did wrong was not bring her to a responsible adult."
Reading along and jumping in:
I think it means that he's saying she was too drunk and he should have made sure she was safe.
I'm not sure she realized what she said; it was at a part of the interview where she was really upset.
I would like to add this: in all the crimes/trials I've watched, that woman is the ONLY parent I've seen who is behaving in a way that I think I would if it were my child (except for the part about making him tell the truth.)
I'd be hysterical!