Hopefully, it's merely full screen. But another possibility is that the shell was switched to Internet Explorer. Normally, the Shell is "Windows Explorer" which is the program responsible for displaying the start menu. It was probably changed to avoid the system being made nonfunctional.
This does put us in a pickle, though- How can we fix it?
Well, one point is that, if Windows Explorer isn't running, running it will bring us the taskbar. From there, it's a bit easier to work with and try to fix the setting. But how do we do that?
There are a few ways. Control-Shift-Escape should allow for running Task Manager, where you can use File->New Task to launch "C:\Windows\Explorer.exe".
If that isn't available (maybe it was restricted too) Another possibility is to download a file from somewhere, or use the "Save As" feature. This will show a Save As Dialog. You should be able to navigate to C:\Windows\ and run explorer.exe. You'll have to right-click it and choose "Run" or "Open" rather than "Select".
The Taskbar should appear.
Now, changing the shell is relatively straightforward. it is a registry setting. Now, one possible issue is if her son also restricted the administrator account. It should be possible to run regedit but it may prompt for a password, at which point we'll be stuck. If it doesn't and you can start registry editor, it will be necessary to adjust the following registry key by drilling down into the folders:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\WinLogon
There should be a "Shell" Value in the right hand pane. It will be pointing at Internet Explorer Windows Explorer can be replaced by putting C:\Windows\Explorer.exe into this value.
