If you somehow know there will be a high chance of OPUP then keep CXGO in booking and use BA to access the F lounge as you said.

If you know that the load is light and opup chance is nil, then Id say keep BA for both, as time and again the onboard service for Emeralds is superior than for CXGO's.

Obviously she will also need to requalify though, right? So you should think about that part...