It is sometimes very difficult to deal with other people’s problems, so only get involved if you think that you can handle it. If your involvement helps her, but as a result you will need outside help, then I don’t believe that you should get involved.
One more thing. If she gets “Horrifically Nasty” again, like she did in the past, I would definitely tell her that she is out of line, and if she does it again, you will cut off all contact. (The only reason I would give her one more chance, is because you did not object the last time, so she may not be aware that she hurt you.)