The best settings really depend on the scene in front of you, for some circumstances you might want to use wide apertures such as f5.6 to separate a subject from the background, if you're shooting in woodland for example. Otherwise, the traditional landscape settings are normally apertures between f8-f13 (probably using aperture priority mode), ISO 100, with exposure compensation to suit, with the camera mounted on a tripod. Graduated neutral density filters will be very useful if your better half doesn't want to process her images and polarising filters will boost colour and contrast in sidelit scenes. Set the white balance manually if shooting jpeg and make use of the histogram on the back of the camera, ensuring there is no excessive clipping of highlights and dark tones. If you want ultimate quality then raw is the way to go, but it is understandable if your wife just wants to take pictures without having to spend time editing in front of a computer. If she ever is persuaded to shoot raw + jpeg, if she compares the unedited raw and unedited jpeg side by side, the jpeg will look much better as the raw will need to be processed.