If the worst of what she's saying is true, then she should have taken the evidence to the police - by knowing of a potential crime and not reporting it, she is potentially making herself an accessory!
If it's not true, and if it was just sexting (or actual physical infidelity) then of course she shouldn't be making stuff up, or as was said above, enabling a witch hunt. That's quite disturbed behaviour, as much as she will be hurt by this, he doesn't deserve that.
I still think however bad a person she is, no one deserves to be cheated on (and imo sexting is cheating), just end the bloody relationship and move on.
Being cheated on by someone you love and think of as your best friend is humiliating. But unleashing hell in this way just makes her look crazy, and risks losing any sympathy people otherwise would (rightly) have had for her.