Why do they have this power?
They don't have any power.
You have.
You have the power to maintain NC - if that is what you wish to do.
She can attempt to lure you, seduce you, tempt you or whatever. But she can't control you.
Assuming everyone understands she is disordered, what she did and what she is capable of (including you) - I probably wouldn't bat an eyelid. I might even shake my head and laugh to myself "Still crazy after all these years"

.
Just ensure your family members or whoever know that you are NC, and not to provide any information about you, other than - "oh, acknowledgement is doing incredible, but very private, so can't discuss that".
You can't really tell them not to have a conversation with her, but you have every right to ask that your privacy be respected.
she just told me to "relax" and "past is past"
People who've not been through a Cluster B relationship just won't get it.
Point them here if you think it will help?
help to stay strong please
You don't need help.
You are strong. Your confidence is just a little shook. Totally normal.
But this quote springs to mind:
Albert Einstein is broadly credited with exclaiming “The definition of insanity is once more trying the same thing you've done over and over again, but this time hoping for something different to happen"
If that doesn't help - just think of promiscuous she has probably been and god knows what she may be carrying *bleurgh*
Could have HIV for all you know.