You can both get upgraded, but it will be harder as your upgrade priority is determined by the lowest medallino status booked on the same PNR (in this case, no status).
It depends on what your goal is - if you want to maximize the chance of one person getting upgraded, then split the PNR, but your GF will no longer be upgrade eligible.
Or if you want to maximize the chance of sitting together, keep the PNR together.
Good luck.