I can't say I understand what she's put you through, so I'm not going to try to be all high-and-mighty about it, but I've had a similar experience, in a way - my husband and I took his ex (and 8-year-old son's mother) to court when she finally pushed us over the edge by saying she was going to move cross-country with their son (who my husband spends half-time with and pays child support for) so her army husband of 2 months could be their son's new "daddy" and that hey, she wasn't even sure my husband was the father. (She and my husband were together for 7 years and she says -that-? B*#?$!) And this is -after- she'd not taken him to school 30 times and been late nearly 50 (no joke) in one school year, not been feeding him properly, etc.
I was so angry, with valid reason, that I really couldn't have cared less how things turned out for her. For all I cared, she could lose complete custody of her son and have suffered forever after that. Well, for my husband and step-son's sakes, I tried to step back from the situation, gather what we had on our side for the case, and let it pass as it would in court. While what she did was wrong, she has both reformed herself in some ways, and gotten her just dessert in others. She played the innocent, naive single mom (although she's married) who had a rough lot in life (came over from Ukraine as a refugee at 8) and the commissioner bought it. She got primary custody.
However, she saw the enormous error of her ways, has at least treated her son better, and realized how important his real father is in his life. Also, as far as her other faults go, like being irresponsible, she's dug her own hole - car repo'ed, telephone cut off, son disappointed so many times he knows which parent he can count on and which parent he can't by age 8. Still, I see now that she is absolutely necessary in her son's life, even though she was being a bad parent for the long time.
It's not the same thing, but as for your ex - if you were to act when you're this angry, you might do something that feels right now because of your piqued emotions, but in the end, might do you more damage than good. Whatever she did, you don't have to support her, but I wouldn't suggest going after her either. Even if you don't believe in karma, actions have consequences, and she'll suffer for hers sooner than you think. I am by no means a lawyer but if you feel legally obliged to disclose whatever illegal offense you believe she committed, you should probably do so to the proper authorities.
Either way, good luck with your path in life - just think hard before you do something you can never take back.