I'm not as much of a fan of The Wing as others are, but in this case I would recommend this. No other CX lounge has more facilities, and I doubt that the new QF lounge would be regarded as clearly better than The Wing. The J entrance to The Wing is at gate level near gates 1-4.

When you return to the airport, clear security at the southern end of the terminal, near the CX check-in counters. It's then very easy for you to go down one level from security/immigration, head towards gates 1-4, and go into the lounge to meet her.

You can then go on to lounge hop thereafter if you feel like it, depending on the gate being used for BA28 (which I believe is less predictable now than it used to be).