I agree that mrs.clinton should have been using secure email for all official communication. But, based on the article above it seems as if many were aware that she wasn't. Not only that, they seemed to be trying to find ways for her to be able to continue doing so. In the government, we all depend on checks and balances (not that it works out most of the time). Why then, wasn't it made very clear that this was unacceptable, immediately? It seems like in the beginning, when this was first noticed, it was brought to Clinton's chief of staff during a large meeting that did not include Clinton. 
She is shown as not wanting to give up her BB. This being a large security risk, why didn't national security make it clear that this wasn't an optional request? Very clear.  It feels like folks were too busy trying to accomadate her that they failed to do their own jobs. 
IMHO, the blame on this issue should be shared by many, as well as Clinton. Good news, she doesn't seem to have been hacked...