What she could not get was a Blackberry. So rather than use the approved device, she decided the simpler solution was to host her own email and just use a off the shelf device? Nothing about this makes any sense.
I just don't believe that Hillary Clinton could not get an email account on a government email server and that somehow having exchange at her house with no controls was the last option she had. I can't think of a scenario where a server at her house is better than almost any other option.