Hating on his new girl?

Ok, I think my cuzzo has gone insane in the membrane. So she's been crushing on this guy since 06 and she's been too scared to talk to him. She used to go to his h.s, she knows where he lives (she's been to his house 3 times), knows his fbook, twitter by heart, and ACTUALLY thinks that they'll end up married one day (Her mom overheard a joke between the mothers in church). I feel for her b/c I KNOW that this is a lost cause. He's dated at least four times and he's currently dating someone else, since april. She found this out when she read a status on her fbook "shoutouts to my babymomma for coming to my crib and cooking for me. I got love for her, she know who she is" She practically broke down when she saw a touching pic of them together. Her parents taught that she needed to go see a psychiatrist. So she decided to create a fake fbook account and stalk the gf. She hasn't done it for a mth now, but her jealousy is starting to resurface and I think that she'll probably go as far as to purchase their background info online (it's cheap, smh). She doesn't care if she loses her friends (they know the gf) or her self-respect in the process, she really wants to be w/ him AT ALL COSTS. How do I get through to her?