Torchsong-
I think you're on the right path. And kudos to you for being committed to making this work. I would suggest one idea. I'd have a "go to place" type command. A bed or mat that your dog will go to and lay down. Make that place a wonderful place for your pup. Pup goes to mat, treats rain down on her. Lots of praise. Slowly increase the duration and distraction while pup is on the mat. Have a command "Where's you place" or "magic mat". This will give your dog something to do while your wife comes over the gate. And if pup is on the magic mat relaxing, it's hard to go into defense mode (as long as the mat is far enough away from the gate).