Nobody can say for sure what gross negligence is but what it is almost certainly not is something that similar people in a similar position have also done.  If other Secretaries of State conducted department business via private email it might not even rise to the level of negligence, let alone gross negligence. That her predecessors did so less frequently, or not on their own personal servers, may (should?) matter to your opinion of her, but it doesn't matter when it comes to application of the law.  After all the potential crime requiring gross negligence would be "permitting removal" of information by having it sent to a private server, and for those purposes it doesn't matter whose server it is or how often you did it.
You all are waaaay too deep on this.  Take a deep breath.  This is a mistake in judgment, and it's fair to hold a mistake in judgment against her, but it's not close to being a crime.  Never has been, never will be.
		
		
	 
I'm not concerned with her or any of her predecessors using private servers to conduct department business.  It's the message traffic that traversed those unaccredited servers that concern me.  Yes, it was a mistake in judgment.  It happens to all of us.  But there are consequences when discussing classified information.
Top Secret:  Information, the unauthorized disclosure of which reasonably could be expected to 
cause exceptionally grave damage to the national security that the original classification authority is able to identify or describe.
Secret:  information, the unauthorized disclosure of which reasonably could be expected to 
cause serious damage to the national security that the original classification authority is able to identify or describe.
These are from Obama's signed Executive Order 13526 - Classified National Security Information.  
The content of her discussions that were considered top secret, were sensitive enough to the point that unauthorized disclosure could cause exceptionally grave damage to national security.  Unauthorized disclosure... if she sent one of those emails to an uncleared person (or CC'd someone or another department), that is unauthorized disclosure.  It being housed on a private, non-secure server is a no-no in itself.  The IT staff (private contractor?) who managed the server had access to those emails.  The potential is staggering.  That's why that type of information is classified and must be protected through specific methods and means of distribution.  
Permitting removal by having the emails deleted/purged.  We don't know the content of those email conversations, but for them to be classified secret or TS, they had to be related to extremely sensitive topics.  Who read them?  Who forwarded them to someone else?  Did anyone print them off?  Is it possible that any of the information discussed could have led to the loss of life or a potential terrorist attack?  Who knows?  No one can say for sure what gross negligence really is, and it appears that different people view it differently than others.
The fact that her predecessors may have done the same thing is equally appalling imo.  If they did, shame on them and I wish they had faced similar inquiries as Clinton.  But they didn't; maybe they just didn't get caught.   I'm glad they aren't running for president.