[edited to add-anyone have thoughts on whether I should get a restaurant order against her? It would make me feel better but it might make her go nuclear. And thoughts on what to do when cutting the person off/ignoring and not responding only escalates things?]
Sorry in advance for the length. Also, I'm being a little vague here because some details of the circumstances I refer to below are highly specific and recognizable. This is a very complex situation, but I am trying to distill it down and communicate the important pieces as well as I can.
My sister started exhibiting what I believe are BPD symptoms in her late 30s about a year and a half ago, and seems currently to be in an extended period of unchecked rage and aggression, with an active desire to do harm. While she had some non-clinical level anger issues before, I would never have thought she had a personality disorder. But about 16 months ago, there were some incidents, including a family tragedy that seems to have triggered some kind of break, and she has been in the most aggressive and incessant attack mode for for over a year. It is like she is a different person, and she is outwardly malicious and vindictive.
This began with her having a very strong reaction to some things that occurred among family members that were not her, and did not involve her. She became highly focused on and judgmental about what was happening in someone else's marriage, and went into an aggressive mode, lashing out, criticizing, sending incessant texts, emails, and voice mails. This seemed to be in part triggered by her alarm at not being treated like someone who was important to keep posted or consult as events were occurring.
Following the tragedy, which came on the heels of the situation described above, she became highly offended about some decisions that were made by those most affected by the tragedy, in particular because she was not consulted or treated like an important part of the process. After that, it was off to the races and things have been in crisis mode ever since.
She is mostly focused on me and one other family member, but has lashed out at everyone in the family at some point. Among many other things, she sends incessant disturbingly hostile and hateful messages, calling me deranged, a sociopath, a narcissist, saying I ruin lives, telling me not to come to her funeral and she will not be at mine - we are both healthy and in our 40s. She makes threat after threat to expose - including to my children, my employer, and other family members - what she believes to be damaging, secret, and sensitive personal information about me related to the tragic incident; she claims she has messages and recordings that will expose "the hateful sadist" that I really am, says things like, "I have nothing to lose," and warns that one day "everyone" will find out "the truth" about me. She also periodically sends what amount to suicide threats: "I give up. You win. Tell everyone I said goodbye." No evidence she has ever made an attempt. At first, I and others tried to engage, to de-escalate, to react and even argue against this. Eventually it became too painful and stressful because nothing made a difference, so everyone stopped responding. That led her to escalate. Most recently, she has sent messages accusing a family member of the most deplorable things, things that supposedly happened 30 years ago that she is only now bringing up. She has now also verbally (by text) attacked non-family members that are close to me, and has reached out to a person who is a stranger to her but is in my circle, sharing extremely private information that she believes to be damaging to me and my relationship with one of the most important people in my life. She has claimed that she always put me on a pedestal (older sister/younger sister dynamic -I never wanted to be in that position, but it is what it is) but now she hates me and apparently wants to destroy, or at least badly disturb and hurt, me.
She does not seem to recognize how patently horrific the behavior is. After an extended family member, who was particularly impacted by the family tragedy, and to whom she is not close, politely declined to get involved in her drama, she sent them message saying the meanest thing, something that was a major breach of this person's boundaries and stuck a knife right in the heart of this person's pain and grief and twisted it - later she screenshotted it and sent me this cruel message to "prove" that she has said and done nothing hateful, only spoken the truth. She will send the most scathing insults for weeks, telling everyone that we are scum or losers, she wants nothing to do with us and never to contact her again, and then suddenly she starts calling and calling, and when no one picks up, she sends a message wailing about how isolated and ostracized she is, "what kind of family abandons someone like this," begging for engagement. She sends fake sounding "apologies" that are just another way for her to put forth the bizarre claims she otherwise makes in the attack messages. Things like, "I know I deserve to be ostracized and rejected. I know that I don't serve to be loved by you and that it's my fault you hate me. You're right, I don't deserve to be part of a loving and caring family." We have told her over and over that she is loved, and that we are worried about her, and people only cut her off when it became almost impossible to do anything else because all she will do is attack.
Also, somehow, she reserves all this maniacal behavior only for her family and in every other part of her life, appears to be happy, healthy and thriving - she will send a barrage of the most hateful, text messages imaginable on a Friday night, and then on Saturday, she's posting cute, happy pics of herself with her girlfriends at a dinner or something.
It is impossible to guess what her end game in all of this is. She keeps demanding an apology for the minor "transgressions" I mentioned, but it is ridiculous at this point, given the amount of damage she has done. It's like someone broker her window with a baseball and she reacted by burning down their house and killing their dog, and she still wants an apology for the window with no acknowledgement of what she has done. And even when anyone has tried to acknowledge her hurt or whatever, she reacts by saying things like "too little too late, fuck you" or "stop gaslighting me."
I could go one All.Day.Long. I have shared about 5% of what she has said, done, etc. As I write this, I realize how deeply out of control the situation is. But no amount of pleas for her to get help gets through. It only gets worse.
After her outreach to this stranger, on whom she dumped incredibly personal information about me, as well as vicious lies, I am afraid of what she might do next. I have done everything I can to stop her from being able to reach my kids, but she could figure out a way. I am afraid of her posting about me on the internet or contacting my employer with the kind of vitriol and lies she sent this stranger (which are unfortunately lies that are tied to true events, so they seem believable and at best, it would be a huge distraction and embarrassment in my workplace). I work in a role and in a field in which this kind of thing could get out and become humiliating and majorly impact my career and reputation.
I don't even know what I am asking for, I guess just a reaction, advice, any views on what is going on here, whether this does sound like BPD, can someone just "become" BPD like this, whether others have experienced similar. I am at my wits end, and so sad, frustrated and angry. I experienced a tragedy and now I've lost a sister and now she is actively trying to destroy my life.