Okay, it's early, and I haven't yet had my coffee, but this thread hits home for me. I hope I can make sense.
I believe that if you have a child in your home that becomes a physical danger to anyone else living there, they must be placed elsewhere. I know its not an easy decision, but we had to make it. My stepson lived with us for 4 years. He was a very difficult child. He was diagnosed (AFTER we got him, and started him in therapy and he saw a psychiatrist) with ADHD, bipolar, and conduct disorder, which is what they call kids who will eventually turn out to be full blown antisocial personality disorder.
We went through hell with him. I mean, HELL. We have two smaller children. The day my stepson pulled a knife on my husband and tried to stab him, is the day he was sent away from our home. We had no choice. However, we still pay a huge sum of child support, more than twice the amount that this mother does, and he's in Juvenile hall. We never disputed that we needed to care for him financially.
This woman will not be able to get out of child support. I don't think that's what she's trying to do, though... I think she just doesn't want any of the other children hurt. We had to make that decision, and it was awful! But she SHOULD have made the decision as soon as she found out about the kids being molested by this teen.