Welcome to FT!

You cannot add someone to a PNR once it's created, and your wife won't be eligible for an UDU if she's on a separate record. The best you can do is either try and upgrade her with your miles (or some other instrument) and then also hope that you clear yourself. Or, call reservations, have her moved to E+ next to you, and tell them to cancel your automatic upgrade request. That will assure you will sit together.