As your fellow sister (
) I think if this woman is indeed a risk management issue (which it definitely sounds like she is), the chapter in question should definitely be alerted of this.
The fact that she's also one of those psycho girls (which it definitely sounds like she is) is also not something you would want associated with your sorority. If she obsessively calls every girl who talks to your ex, every person in school will know her as "that girl" who also happens to be an ADPi.
As horrible as it is, 1 person can label an entire chapter because of the actions of one girl (or guy in a fraternity's case), and call me crazy, but I don't think the "psycho druggie" sorority is a very desired label :P