If information is confidential, it should be handled with discretion.
Actually, it should be handled according to the law. Confidential information is classified because the release, even if unintentionally, will cause damage to national security.
There is circumstantial evidence that she had Special Access Programs (SAP) installed on her private server. These programs contain the most sensitive national security information. These programs would be installed on a secure computer system and housed in an area where you would require special credentials to access the area where the secure computer system is stored.