Keep in mind you may not (probably won't?) keep any confirmed PlusPoint upgrade when you switch returns. I also don't know if United fixed the "feature" where a split PNR keeps/kept the status from the original PNR.
You might want to book both of you on the flight your spouse ultimately wants to fly, then once her UG is confirmed, switch yourself to the flight you want, and then you'll be on the UG list as a 1K. (Not sure what the order of flights is.)