Quite simple to get around this, Rowan. All you need to do is create a Desktop Shortcut for each of your PAF databases (not the program's ".exe"). Then when you want to open PAF to view your database click on the shorcut to your data. Your wife would just click on the one to hers.
Create the shortcuts by locating the ".paf" files for each, where ever you have them saved. Place your cursor on the first one, hold down the right button and "drag" it on to your Desktop. Release the button and select CREATE SHORTCUT HERE. Repeat for the second file.
To simplify using the shortcuts, just rename the icons with each of your first names.