I am so sorry to read of your experiences. Surviving the experiences of an abusive narcissist is a lifelong endeavor that requires a whole lot of time, patience, and brutal honesty.
With regard to your mother's choices, the only thing that I can offer is that the "Perfect Victim" is often the blindest human being of all - they choose to believe that every human being is salvageable, good-at-heart, and deserves every benefit of the doubt. This simply is not true. There are human beings out there (rough estimate is 22%) who live their lives without any conscience, remorse, or empathy, and will do and say whatever it takes to get whatever it is that they want. The "Perfect Victims" of this world refuse to recognize that there really are BAD PEOPLE with malicious intentions right out of the gate. NPD's and sociopaths target, lure, they use, and discard, and that is their primary function in this worldly life. More importantly, accepting that you cannot control or influence your mother's choices or opinions is the first step toward your own healing path. The only person that you can control is you - period. You are not responsible for the choices or beliefs of anyone else. You are only responsible for your own choices and actions.
I completely empathize with your situation - my mother believed that I was a "bad person" because I made the difficult choice to divorce the ex-sociopath abuser. She believed everything that her son-in-law told her, and it was strictly her choice to believe him, rather than her own daughter. My father did, as well, for a short time until I told him everything that had transpired during our marriage, including liquidating our children's college funds to purchase cocaine, etc. I took ownership and responsibility for my choices to go along with that monster, tolerate his brutalities, and cover up for him when I should have filed complaints. For that, I expected to lose my father, entirely, and I was quite prepared for it. What happened, instead, was that my father gained an adult-based respect for me for my having disclosed truth, even when it made me look like a horrible person, as well.
For me, the only solution to NPD or sociopathy is to walk away, regardless of whether it's "family" or anyone else. To me, the definition of "family" is not shared DNA, but being surrounded by human beings who encourage, support, guide, and speak truthfully to me without any hidden agenda. That is the definition of "family."
You may wish to consider individual counseling for a while, just to help you sort it all out. The best way to locate a counseling therapist for this particular job would be to contact your local "mental health" hotline and specifically ask for a few counselors who have experience and knowledge of domestic violence/abuse, NPD survival, and sociopathy survival. There is also a website that is devoted to the education and healing process of sociopathy survival: www.lovefraud.com Surviving malignant narcissism and sociopathy is a very, very difficult process that cannot be successfully accomplished, alone, in my most humble opinion. Reaching out for assistance does not make me crazy, helpless, or stupid - it just means that I am courageous enough to know and accept my own limitations and that I am willing to do whatever it takes to step onto my healing path and move forward so that I will be less likely to be victimized, again.
My very best and positive wishes to you on your healing journey.