Pat woke up the other day and all her emails had vanished from her Gmail account. She uses her web browser to check her mail every day, clicking on "all mail," first, then deleting and emptying her trash. Leo says that she doesn't ever need to delete her email or empty the trash. Trash gets automatically flushed every 30 days. Leo suspects that Pat may have accidentally deleted more than she thought. For instance, if she hit command A, that will select everything and then delete. Unfortunately, Gmail is a cloud-based option and there's no real backup other than that. So when she deletes something, she's deleting it from the cloud. Moving forward, Leo recommends not deleting anything!
Also, on the outside chance that someone else has changed her password and deleted her emails, it's a good idea to change it again and then set up 2-factor authentication. That way no one can change her password without her knowledge.