Help Unlocking Desktop Settings

My friend's little sister found her way onto her computer yesterday and apparently messed with some settings that she shouldn't have been messing with. Now my friend's computer is acting as if it is locked, and she is unable to change any settings, such as her desktop properties settings (wallpaper, etc.) I think it may be the same kind of locked setting they use in schools and libraries to make sure people don't mess with the settings on the PC. I looked around but I couldn't find where settings such as these are located, and she's desparate for help. Does anyone know how to remedy this?

Have you checked under Administrative Tools > Computer Management > Local Users and Groups > Users > *user name* to make sure the person has admin rights? They should be a member of the Administrators group.