Without a specific Email address to track it is all lost in the noise.
Taking the 5th and trashing her hard drive hides the Email address she was using. Specifically it hides the connection between her and the Email account wherever it was.
So to me, the key is finding out what the Email address is and therefore where it was hosted. If it can be found, the Email can be retrieved.
Finding it I believe is possible based on the IP address of her computer/office. With that IP address the hosting companies can be searched for whatever accounts are associated with it.
And then all will be exposed.
If they were using free email accounts, then the emails could have never been sent. A popular form of email communication among bad guys is to share an email login with other conspirators. Then, an email is composed, but never sent out. It is saved as a draft. Accomplices can login, read the draft to obtain instructions, and leave it parked as a draft for others to review.
The big picture lost in all of this scandal is that emails reside on SEVERAL servers (there are backup servers PLUS there are each of the RECIPIENTS’ servers as well...)