Summary and details of the problem
I have a friend who is pretending to be the girlfriend of a rich closeted gay guy. I think I can empathize why they are doing this. She enjoys being the talk among of all our friends and being able to influence trends and opinions among us just because she is now hanging out with lots of rich people. Her boyfriend doesn't have anyone questioning his sexuality (or possibly being harassed). However, one of my friend's enemies found out the relationship is a big fake from the rich guy's ex-boyfriend. This enemy is now planning to send out all the texts/emails/conversations/photos of the rich guy's past gay relationship to expose my friend and her boyfriend as both liars and frauds. For context we are all still in high school.
What I've tried
I talked with my friend's enemy. From what I was able to gather, she is doing this to get revenge because she believes my friend "ruined her life". Based on my analysis of her personality, I think she liked being the center of attention. Before my friend started dating the rich guy: friends consulted her on fashion trends, asked her advice on their problems, was the first one to be invited to a party, etc. After my friend started dating the rich guy, she felt she was pushed aside, ignored, and forgotten. Nobody was paying attention anymore to what she was wearing, nobody was asking her for advice to problems, and people were forgetting to invite her to parties. She saw my friend as the one who took all that away from her. She even complained about how everyone was telling her "[my friend's name] this, [my friend's name] that." Almost every conversation brought up my friend and something about how great my friend was.
I talked to my friend after I found out the truth. She denied everything and called me a jealous liar. She doubled down on the lie and started telling everyone she and her boyfriend was having sex once a week. I tried again asking her things like "why do you want people to think you slept with a gay guy". After a heartfelt plea from one childhood friend to another, she decided to tell me the relationship was fake. She explained to me her reasons. Growing up she always felt ignored. Nobody really talked to her. She felt invisible and nobody cared about her. Her fake relationship with the rich kid changed everything for her. She suddenly felt "loved". People wanted to hang out with her. She had friends inviting her to parties, movies, and trips. People wanted to know her opinions and thoughts. I think I can sympathize with her.
I tried talking with my friend's enemy trying now to reason with her. She didn't care. She believed my friend "stole" all that from her. She is only getting back what is hers. Once my friend is exposed as a liar and humiliated she "will be back where she belongs." She said they are both lying to the world. She even said this would be good for the gay kid because gay people should out themselves. She said this isn't the stone ages and gay people aren't being killed/harassed/discriminated anymore. She already has a private web page set up that has all the evidence to "take down" my friend. She plans to make the web page public and send the link to everyone we all know through facebook/twitter/email/text during my friend's big 18th birthday party. I told her I would tell her parents what she was planning to do. She said she already told her parents and they agree and support on what she planned to do.
I've already tried but failed. Is there any other way I can help convince her not to get revenge? I don't want to see my friend humiliated like that.