OK, as I see it, she was in charge of a department. That department has now been investigated, and it was said to be criminally badly run. She ran it. The buck has to stop at someone when things are so badly wrong that children suffer and die (and its not just Baby P, lots of other children were endangered). The court case seems to imply that it was so badly run, that a case of this nature was almost inevitable.
She was in charge.
She takes the rap.