Victims of Psychopaths Community Group
Is he or she a sociopath or psychopath? Think we're only talking about serial killers here? Psychopaths, sociopaths and even narcissists come in every walk of life, every career level, and every socio-economic category.
For me, what helped move me from pity, concern, and the feeling I had to take care of him; to looking from afar at essentially a machine seizing on me to get anything of value I could offer -- was to read, read, read about them, what they do, and how they do it. When you see the mechanics, the emotion goes away. When you see more clearly just how they are trying to manipulate you, you can try to avoid it.
Basically, beyond some point, it's not your problem any more -- again, depending on what your relationship with them is/was.
The more you think of her as a parasite the less you may feel worry. But to reassure you, I definitely spent years worrying about the psycopath in my life. He happens to be 22 years older than me and one of his favorite things was to talk about a possible heart condition (he'll most likely outlive me he's that healthy). He lives alone in a 5,000 sq ft home and I used to worry he would have a heart attack and no one (because he has no friends) would find him. I worried on all major birthdays and holidays about him wondering if he were happy or celebrating. Somewhere along the line I realized I was worrying about him more than he worries about himself! Because I was projecting my real human emotions on him and how I would feel in his shoes. But they don't feel like we do so it's pointless to worry. They won't even know when you stop worrying because they don't think about you at all! I think when I finally realized all of that then I stopped worrying. It feels cold and horrible to cut off my empathy for my psycopath but it's a matter of survival. Good luck you and enjoy your now more peaceful life. Don't worry yourself sick. she is not worth risking your health and your enjoyment during your time here on planet earth! (That's another thing that's helped me... we are here for only such a short time... I ask myself constantly if I'm only here for maybe 80+ years - how many am I willing to give to this emotional vampire? )
Hope some of this helps.
She might also tend toward Borderline Personality Disorder (BPD). This can co-exist with being a psychopath. People with BPD can act very crazy and abusive to those around them, and they can self-harm ex. (cutting, eating disorders) and are more prone to threatening suicide and sometimes trying it. The most common abuser PDs are BPD and Paranoid PD (ex. excessive jealousy). You might read on BPD too, to see if that helps.
With BPD too, no amount of logic is going to help. Giving her support, if she does not want to change, will just engulf you endlessly and completely. But talk therapy and especially SSRIs do help, so if that's the case, she could maybe get some help and improve.