Seems like there are rules against doing that
More than one
Indeed there are.
You are not permitted to send/receive classified communications, in any form, from a device not previously certified for that purpose.
Any communication is only as secure as the weakest portion of the communication chain. To send classified emails from her smartphone, she would have needed the appropriate encryption keying material on the phone.
If you are going to have classified/unclassified information and communication on a single device, that device requires an approved RED/BLACK separation method. Was this done? If not, any and ALL of her classified emails were subject to compromise.
Furthermore, her smart (at least smarter than the user) would become permanently classified at the highest level of information/communications stored/sent/received.
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