I know how hard this can be Although, cursing is a bad, bad idea. Like you said, it will backfire, the three times three rule tells us that what we send out comes back to us. If we send out good, we'll get good back times three. If we send out bad, we'll get bad back times three. Curses only end up hurting you more than her.
Personally I suggest the best thing to do is give it up to fate, Let the Goddess of Justice decide what she should receive for what she's done. I often turn to the Morrigan - Celtic warror Goddess who decides fates. Let her take care of it.
Also, if she won't leave you alone, try banishing her from your life. or at least banishing her influence.