It’s really very simple. She ordered a colleague to remove classified markings and to use a nonsecure email channel. In addition to her own illegal use of a private email address and server, she directed others to double down on the lack of security and do so themselves. Her job, in part, as Secretary of State was to guard state secrets, and pretty much everything she wrote or received would qualify as such, for what should be obvious reasons.
Nonetheless, she put her own political convenience–namely trying to avoid creating a paper trail of records subject to FOIA requests subject to discovery by historians, journalists, and government investigators–above the nation. She is disqualified from office and a disgrace.