Giga, you are my hero. I love posts like this. No sarcasm, btw, I completely agree with you.
DeW, hang in there. Don't take this person back you deserve so much better. Yes, its sad for her child, but how much more sad would it be if you stayed and grew to hate each other for what happened?
Some doors are one-way. Once walked through, there is no going back. All you should do now is hope she has learned this lesson well enough that she never does this again. If you have the mental energy, you could even make this point explicit if you think there's a chance she isn't self-aware enough to get it.