Hi mrdc. I’m really sorry to hear of your loss. I can only say that i know this works - my ex boyfriend passed away (as i’m sure that you can see from my past posts) and i have seen him in normal dreams and in a couple of lucid dreams.
Just ask your girlfriend to help you - and i would also suggest that you don’t expect too much too soon - i’m sure she has stuff to do where she is too - just have faith and know that when the time is right it will happen for you.