She's nothing more than a bully, and bullies aren't worth your time. Every time she messages you or tries to contact you, erase it(don't even read it, really) and block her. If she talks trash to your face, smile, keep your chin up and walk away. Drama, for the most part, will die faster if you avoid adding fuel to the fire with a negative reaction.
If it comes down to it and the harassment is too much, make a new Facebook, block her and any accounts she's used to contact you. Only add people you -trust- not to inform her of this account.
There will always be jerks out there who want to mess with you, simply because they feel entitled to. If you react violently or become emotional and try to bite back, they get some sort of thrill out of it and continue. But if you're able to keep your cool, breathe, and walk away from it, people will see that you're the bigger person and the abuser will eventually move on to someone else.
Surround yourself with supportive, true friends. People who won't play childish mind games like this with you. It'll be really good for your overall health to have positive people in your life. Trust me, dude, you will make it through with a lot less stress if you can find positive influences.
Good luck, mate.
