It could be several issues, but my first guess, since the FZ1000 is a superzoom bridge camera, is simply that when you zoomed in on your wife's face, you may have inadvertently moved the minimum focus distance of the lens past her. If you're not in macro mode, at the wide end of the lens (zoomed all the way in) you can focus as close as 11.8"/30cm, but zoomed all the way in to the telephoto end of the lens, you can only focus as close as 39.4" (100cm), and if your wife was closer than that, the lens can't focus. That is, the more you zoom in, the farther away from the subject you have to be to achieve focus.

The second thing is that you may not have control over your autofocusing system. You can set the autofocus mode in your camera to use face detection if you want to autofocus on faces. Or you can also choose to use a single area or pinpoint area (see page 40 of the manual) if the AF system is selecting the wrong things to focus on. This lets you select a specific area of the frame for the camera to try and focus on.