She wasn’t “storing” them, she was sending them to someone, after taking great pains to receive them with the classification removed.
In fact, it looks like she was trying to figure out how to delete them permanently so as not to be caught.
How can you delete them if you’re not storing them? If someone is hacking your email server it does not matter how long the email is there. It’s compromised no matter how long it was there. End of story.