I found a website called "Out of the FOG" and that is where I found and read a lot about NPD but there is a lot of information available on the internet. I just searched for NPD mother or narcissist mother and read as much as I could. If I got to stressed I left it alone for a day or two and came back with a clearer head.
I also bought the book "Will I ever be good enough?" and that helped a great deal. I just sat with it and my highlighter and could really relate to a lot that I read. I learned their are different types of NPD mothers but the feelings we go through are pretty much the same no matter what category they fit into.
I would advise you to do the same. Read up and soak it all in. The more information I got the more it made sense and reading others peoples stories and struggles helped me get validation.
There are also NPD groups on Facebook but some of them can display a lot of hate and anger which I totally get and understand but as a recovering alcoholic, resentment and anger has no place in my life today so I avoid those groups.
It really comes down to what you want to learn and what you want to do with what you learn. Like recovery, it is your personal journey and you get to decide what suits you the best for your life.