I feel like given all of the information we have, it's a much bigger assumption to think that the sister is not highly narcissistic.
The label will most certainly help InRainbows, because if she was fully aware of what she's dealing with, she wouldn't be asking "how to help her sister to stop feeling like a victim" because she would realize there is no helping her sister. Best you can do is disengage.
The advice you give, telling the sister stuff "firmly and kindly" is almost condescending. It assumes that InRainbows hasn't already tried something so simple and basic within this past year and a half. And stating it one last time will change nothing at all.
You seem really uncomfortable with the idea that a parent could be estranged due to their narcissism.
I don't mean to argue, but your viewpoint is actually very counterproductive and not based in reality. Does it matter if the sister is actually a narcissist or not when she is behaving exactly like a narcissist would in this situation? The advice for dealing with her is all the same.
Disengage as much as you can and lie if it makes interactions with her easier.
What job would you do now, if you had the choice? (Light hearted)
Rejoice! Chancellor Healey Will Give Us Cheap Marmalade & Gherkins.


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