<human>: Give me the gist of the text in a nutshell

Background:

At a university, a girl in my dorm hallway (let's call her Rachel for privacy) liked me. I liked another girl much more and generally believed that Rachel was very fake (insane amounts of makeup) and attention seeking to an extreme degree. In an unexpected twist, in a desperate play for love and attention, she played the sympathy card and told me she had been raped a few months before college.  She didn't do anything about it. I insisted over and over again she go to the police and get the ball rolling but she was afraid the guy would hunt her down and hurt her. I felt bad, but it didn't change the fact I had already disliked her.

That explained her crazy emotions. 

(Insert winter break)

We come back from break and she goes off the wall, having double digit one night stands in a month, including sometimes multiple in one night. I don't use the term lightly, but she became a slut. I attribute this to it being her 'get away' from the pain.

What I didn't know till the last week of school after her crazy sleeping around habits continued, her best friend told me she was worried about Rachel's sleeping around because Rachel has aids. Best friend (lets call her Kate) didn't know how she got it, but confirmed she had it. Kate doesn't know Rachel has been raped. 

Now I'm the only one who has the complete picture and Rachel is actively ruining lives and I don't know if I should intervene. 

Keep in mind: Rachel and I are no longer friends or even talking because of our personality differences.
<bot>: Girl got raped, contracted aids, now spreading it wildly. I'm the only one who knows all of this and don't know how to stop it.