Your wife sounds similar to mine actually. But I've given her specific instructions for the walkie. Hold the talk button down, BEFORE I hit something, simply say "stop", I stop, she releases talk button, and then I ask her for further instructions. And I keep it simple by using drivers side, and passenger side. Don't want to over complicate it with "left" and "right" haha. I have her stand directly behind my fiver though. No need for me to see her, just for her to be able to see both sides and the rear to ensure I'm not going to hit anything.
One thing I learned by driving a big rig is ALWAYS, always, ALWAYS pull up further past the hole you're backing into than you really feel that you need to. Because backing up another 10 ft is easy, but if you didn't pull up enough by 10ft, it's a lot harder and you'll probably have to start over again.
Blind side backing (which is the technical term for your diagram) is the hardest side to back to. No questions about that. If you have power mirrors, turn that passenger side mirror way out while you're initiating the turn, then when you feel that you've maneuvered it to where you need your mirror back to normal, apply the brakes, adjust mirror, and back up more.
Trust your mirrors. Trust your wife. If you try it a couple times and fail, go drive a loop around the campground, take a few breaths and try it again. Remember, this is suppose to be a relaxing getaway!