My take is she got minimal legal advice. Hillary was a sloppy, do nothing Secretary of State who was constantly flying around aimlessly to visit foreign leaders her first few years in office. I can see Hillary and Huma cackling over what a stroke of genius it was to have her own private server so she could discuss Clintoon Foundation fund raising and other matters without Obama administration gofers snooping. Maybe Sidney Bluementhal came up with this idea.
My take is the same as yours. Too much ego to have an expert look at the issue.