P - as another daughter of a narcissistic mother, I can definitely relate to the feeling of being at the edge of an abyss! Unlike Anika I always knew my mother was mentally ill (diagnoses from several therapists, she never went to one long enough to make any progress though, and usually managed to place much of the blame for the stress she was under on... you guessed it... her kids). It makes very little difference to me now, as an adult, to know that she's mentally ill. I understand her better knowing that she's a narcissist, but deep down, it doesn't change the fact that she never made a true effort to change, and never listened to her children.
Personally, I needed to listen to my gut as an adult and
stay away from my parents for a long time. I considered cutting off all contact, but eventually settled on only talking with them when
I feel like it. This was difficult, as I felt pretty selfish for doing it, and my n-mom's favorite thing to accuse me of as a child was selfishness. But slowly, it was as if my sorely abused inner child finally started to feel respected, and came out of her shell - she knew I wasn't going to let her be attacked. (That may sound a little weird, but it's the best way I can find to describe it

) It all happened at the same time that I started reading up on narcissism on the web and in books - a big thanks to Dr. Grossman for his website, it really struck a chord with me, still does.
Now I manage a phone call with them once a month or so. They try to call twice a week, but I let the answering machine get it. I live far enough away that they can't drop in on me without notice, although a year ago they managed to set up a near-surprise visit, for two weeks, that drove me raving mad. During that visit I set boundaries with them, in front of my husband. They promptly crossed them a month later with one of the most scathing, ruthless character assassinations I've ever experienced, so I restated the boundaries, cut off contact for a while, and ever since they've been manageable. Barely. My mother still launches an attack out of nowhere every once in a while, but by email since she can't get it out of her system on the phone anymore. The nice thing about email is that there's no terrifying face and voice behind the words, y'know?

That and you can hit "delete"! It's a lot easier to see that the attacks are totally out of touch with reality when you can re-read the words a few times. That helps too, realizing that no, you didn't make up all those outrageous attacks from your childhood (my mother always told me I imagined the worst things about her and was an awful, selfish, lying, ungrateful child for it...

)
Best of luck with your mom

In short my advice would be to follow your gut feelings, don't betray them!