Yes, I came to PC because of my experience with a covert malignant narcissist...possibly a dark triad with dominant traits in machiavellism.

One time, I set a firmer boundary than usual (yeah, I'm a softie and not good at saying "no").

Well, it would have been better if she rashed out on me in denial or gaslighted me since her true color would have shown. At least I would have a tangible sign to point a finger at. But no, nothing obvious like that.

She apologized and evern appreciated me for "informing" her, and appeared to be very understanding. She even complimented me on what a wonderful person I am. It seemed too good to be true based on the pattern of behaviors I have seen over the years (since she holds grudge against others forever when she doesn't get her way).

And it was too good to be true. Because soon the passive-aggressive retaliation came my way.

You can never think that you are the narcissist's exception. If she has done damage to others, she will eventually do so to you also. A narcissist is not loyal to anyone except herself...if even that!