My wife also drive forward only. That's okay with me as sometimes I really need a break. When we took the ferry from Skagway to Haines, we ended up in the bow of an amid ship loader. She didn't really enjoy the crossing and was a little pale as we returned to the rig. She couldn't see how I was going to get out of the ferry.
She figgeted and cringed and sweated as I backed up only using the driver's side view mirror. As we left the ferry she asked me how I managed to back up about a hundred feet only using one mirror. I told her it wasn't me it was the deck hand, he stayed on the driver's side and he kept me from hitting anything. To which she replied, "but you didn't talk". I told her he gave clear concise and positive directions with his hands and eyes just like he has for tens of thousands of big rig and RV drivers.
Now when I back into a back in only space, she only show me when to stop and smiles the entire time. She won't back it up but she is really good at telling to stop doing things.