All widescreen TV's will have button on the remote control to manually select the desired picture aspects (screen size). Usually providing the option of 16:9; 14:9; 4:3; cinema; panaramic, subtitle mode; or Zoom, along with auto aspect setting.
Also, the default setting for picture aspect, whether it's automatic or forced 16:9 may be found as a seperate function within the TV's menu system.
If you've tried every setting, then you will have found one which changes the picture aspect as described.
In that case, what is the effect you get when changing the picture aspect?
Also, if a Sky or Freeview decoder is being used for reception, ensure that they are also set to 16:9 (widescreen in their own on-screen menus).
Dark scenes can sometimes, temporarily, confuse the auto-aspect switching.
Otherwise, problems involving over scanning are usually due to failure of the frame circuit (incorrect vertical scan) or low EHT-very rare.
The problem with your girlfriends TV, sounds like its aspect is set to 4:3 screen ratio, either manually or by it's auto aspect switching.
Cobweb, May 2006