recovering unsaved documents after restart

Computers do not restart "randomly." They restart after installing updates, and generally they give some warning before doing so. If the document was never saved, it's unlikely there'll be anything to recover, but your sister can avoid this situation in future by changing the Windows Update setting. Most likely she has it set to the default (and recommended) setting of "Install updates automatically." She should change that to at least "Download updates but let me choose whether to install them" or, even better, "Check for updates but let me choose whether to download or install them."

I prefer the last setting because I am offered many updates I don't need; because I have several versions of Office installed, I am offered updates to the Junk E-mail Filter for three different versions of Outlook even though I'm running only one version. Since I have a painfully slow Internet connection, I don't want to download updates I don't need. With either of these settings, however, your sister will get a chance to decide when to install updates and will be prompted to restart Windows, but she will have plenty of time to save files and close running programs.