The only mystery that concerns me is this:
Your EMAILS are not stored on your hard drive. If you think they are, disconnect your computer from the INTERNET, then try to access your emails.
Now, you can DOWNLOAD and SAVE your emails on your hard drive, but there would be a trail of that if they were downloaded from one of the .GOV servers.
It depends. Using MS Outlook, you can create a local “.pst” folder to hold all your mail or copies of your mail on your hard drive.
If her account is in fact a Yahoo account, you can use Outlook with Yahoo Mail for a monthly fee.