My experience is that narcissism cannot thrive in true recovery. So something must be missing. I think it gets to the same core issue of discovering and accepting SELF.
With my NPD relationship, I had to go virtually no contact for my own sanity. I'm not in a healthy enough space to battle with it, though I can't avoid minimal contact. You can't reason with irrational, and it's the same thing you get with an active A...their loss of control, guilt, secret self-hatred ends up in them lashing out and confusing you or making you angry because you don't deserve it.
It will not END unless she seeks help--and even then, the stats aren't pretty. There are arguments that NPD is hard-wired from birth, though I personally believe the arguments that say something happened early on where, to protect themselves, they buried the horrible hated self deep inside and created an alternate persona they project to the world (often at a young age). It becomes more and more burdensome to keep the facade from crashing, and to keep the world from seeing their inner "hated" selves...so the control, rage, and lies get worse. Often they rewrite history to fit their "world"...because it's natural to them. Everything you do and don't do is a perceived criticism, and they actually cannot separate themselves from others (which is one reason your "failures" can be so despised...because it's not fitting their picture of reality and is "their failure").
There is no winning in these relationships. Some can "recover", but it's a HUGE road...not unlike addiction itself.
Unfortunately I could write a book on this topic! I've read way too many.
What HAS worked for some in my family is to create very firm boundaries much like with an A, limit written correspondence (if necessary, one sentence emails getting only the point across- NEVER defend a position or respond to their rants, simply delete and ignore), and keep to very small cordial interactions that never get past light surface topics. Never engage. The minute it starts, say "I'm not going to discuss this" kindly, and physically walk away from the conversation. Repeatedly. Responding to anything gives it credibility as being real or having merit--so don't! It's incredibly hard, but effective.
They can't always heal, but they can be trained to what you will accept and respond to. It takes a long time, but I've seen it work, and it's empowering. I should point out that of course they get angrier and more controlling during their training.
But there is an "other side"!