Yeah, my bf got "demand" letter for him to pay what his ex went in w/ false papers saying he was to pay. She lied about custody, her work, income, every factor. They were on him in a minute w/ a stern demand that he pay his child support.. when he's got the kids most of the time, and has none to pay !
He went in w/ proof otherwise, they commisserated with him, but did nothing. He had to actually file against her. Wouldn't you think the child support agency would have done something about fraud??
In your case, I'd make sure you file against her w/ Child Support Office. Just have it on the record at the least. Who knows, sometime down the road she may be working at a reliable job and you can re-coup some of the money to help w/ future costs, reimbursement, college or something. I think there's more criticism of a deadbeat dad in terms of financial support, but more criticism of a deadbeat mom for not being w/ her kids, involved, taking care of them. Should be equal.
You'd think if that Child Support Office realizes you are not getting some income you are supposed to, it would affect your ability to pay the other. Making sure all is revealed to them may be your best bet. Good luck.