That sounds as if she deleted the launcher - the homescreens, dock (the apps at the bottom), etc. Just go to
Google Play on any web browser (in any computer), log in as yourself (login and password from your Google account), then download a launcher. A lot of us have been using
Nova Launcher for a long time, and the free version works just fine. (You can also install Samsung launchers, to get back that TouchWiz feweling [although I can't stand it - but my wife loves it].)