Hi Troubledone
In general, I really don't like to give advice. When I respond to posts I more tend to just relate my experiences. I have made a lot of big mistakes when dealing with my addict. I helped to create a very messy ugly situation. I take full responsibility for my part in it all.
From what you wrote previously, its clear your niece is unfortunately not sober or seeking recovery.
In my experience with my addict, she was never sober or ever seeking recovery. Because of those facts her & I were never able to have any type of normal healthy relationship. It all ended in a disaster.
I wish you the best of luck.