You can't say there's a basis for a violation of a particular statute unless you satisfy ALL of the requirements. Not just gross negligence in general, or in handling email, but specifically in having been "entrusted with or having lawful possession or control of any document, writing, code book, signal book, sketch, photograph, photographic negative, blueprint, plan, map, model, instrument, appliance, note, or information, relating to the national defense ... through gross negligence permits the same to be removed from its proper place of custody or delivered to anyone in violation of his trust, or to be lost, stolen, abstracted, or destroyed."
Again, I'm not aware of anyone ever arguing successfully that receipt of email at a private server constitutes "permitting [information relating to the national defense] to be removed from its proper place of custody." You can make the argument if you like but that's a big stretch IMO for a statute that clearly intended to apply to physical removals, and lawyers don't prosecute based on stretches. And the other statutes require intent, so those are nonstarters.
I've been saying this is how it would go down for many months- that she made poor decisions but her behavior probably didn't violate a federal criminal statute unless you stretch some stuff beyond what it's been applied to so far. Looks like I was right.