860B is Chinese phone. Your phone should be Chinese version but, person you bought it from change the rom to G unofficially. So, you cannot update your phone to G roms with flashing update.zip same as your girlfriend. You can safely flash A roms on your phones or unofficially install G rom on your Chinese phone, that as it's not official way risk of it is a few percent. (No report of brick with installing G roms on Chinese phone except if people did not follow the tutorials correctly or do something that was not in tutorial "installing G rom on chinese phone" by their own

Yes you can update her phone easily with no problem to a "A rom"