Nancy keeps everything she's written on her Yahoo documents. How can she back them up? Leo says that they are already backed up by Yahoo.
The only thing she could really run into is if Nancy lost access to her Yahoo account. Leo advises getting a Microsoft Live account at get.live.com and then set it up to copy over to Skydrive. Another option is GMail. She could sign up for a Gmail account, and then have gmail fetch all of her email from Yahoo. Then she'll have all of her emails backed up.