LaVerne updated to OS X El Capitan and now her email account has been wiped clean. Leo says that doesn't mean the email is missing. The messages are probably still on the server. It just means that since LaVerne is using Apple Mail and linked it to GMail, El Capitan probably missed a step in linking the old email. Other El Capitan users have reported similar problems.
LaVerne should go into the account settings and disable all the accounts. Then exit out, go back in, and re-enable each account so that Apple Mail will re-download all them. If that doesn't work, he should delete the account from Apple Mail. Then re-add each account. Apple Mail will re-download it just like the first time he created the GMail account through Apple mail.