When to fight, and when to back down Options

[MissFits]

There is this girl that used to date my fiance.
She still writes him up on myspace every few months and tells him she still loves him and takes any opportunity to talk shit about me.

Recently her boyfriend got sent to jail and she sent a message to John saying that now that Nick, her boyfriend, was in jail and they should be friends now. She kept saying things to him that made me uncomfortable and I wrote her a message that wasn't rude at all but asked her politely to get the f**k out of our lives. She suddenly got very defensive and started verbally attacking myself and my friends. I then sent her a mean spirited message back that told her if she had anything to say to come say it to me because I was at a pretty well known place in my area.
She never addressed my offer to talk face to face but continued, rather, to talk shit via myspace about various loved ones I have and then she crossed the line when she made a comment about my dad killing himself.
My dad died of a drug overdose 2 years ago and it was a complete accident. It straight up INFURIATES me that she would go that far, but it is not the first time she has done it. I forgave her the last time because she had moved to New York and there was nothing I could do about it.

Now she is back in my home town. She still writes my fiance on myspace and has her one and only friend talk shit to me and about me any chance she gets. Normally I would just crush someone for doing these things but the problem is she is 17 and I am 18. That is assault on a minor and it's a felony. I am not trying to go to jail for 6-12 months for this bitch, what do I do?

[S-Majere]

You can't be serious.