There is so much "narcissism awareness" on the internet these days. By glancing at this person's thumbnails I think I already have an idea of what they're about.
Frankly, it all makes me sick. I'm someone who's lived with serious "narcissistic abuse". It doesn't give me license to dehumanize people. It doesn't give me the right to assume narcissism every time someone disagrees with me. It doesn't mean I need to use empathy as a weapon. All of these things are also narcissistic. It's exactly how my abuse-ringleader recruited us into their machinizations. Exactly. Step for step. Pound for pound.
In other words, two(or more) cycles of abuse don't make a right.
All abuse starts with one critical step. Deciding that the other person deserves that abuse. That way whatever we do next can be justified as "because of them".
I'm not going to take that first step. I know where it leads. More importantly, it would be an insult to my strength. It would mean that the abuse won. It didn't. Love won. Love is winning.
I'm sorry that your sister is going through pain. It takes a special kind of pain to be drawn into the rabbit-hole that she's in. She's trying to set some sort of boundaries. And needs to feel safe in order to do that. Good boundaries are a noble and worthy endeavour. I'd argue that the key is not in "beating enemies" but in "winning at friendship". Or something like that.
I'm only referencing my own feelings so best see my thoughts as anecdotal. I haven't done any empirical diligence. Just my own philosophical thoughts. Actually, this rant has been brewing in me for a while. Thanks for the invitation to spit it all out.