Chances are that program has "stolen" the association to Image files when
installed. You can change this in Windows itself, but it will then affect
your wife's viewing of image files that should open in that program.
To change what program opens files, go to Windows Explorer | Tools | Folder
Options | File Types
In here you can scroll through the list and find file types (GIF, JPG, etc)
and change what program will open them.