Hi Michael H
Good for you for looking out for your girlfriend's health!
Check out this post about banaba tea, I have never tried it and have no experience whatsoever, so you should research it fully to see if it is ok, but it makes me hopeful for my mother who has only 18% kidney function. I will be checking it out myself.
Read the entire thread, there's another post in there about someone who was in the hospital who could not urinate, taking the tea helped a lot.