Not Getting Child Support.?

My husband and I have full custody of my stepdaughter and live in Indiana. His ex-wife has not paid child support for almost two years. When we were getting it, it was not regular and she was far behind. When she does have a job, her wages are garnished, but she never holds a job for more than a couple of months at a time. Her county takes her to court every three months because she is an estimated $10,000 behind. However, she just gave birth to welfare baby #4 and, because she is on TANIF, they cannot demand that she pay, although her balance will continue to accumulate. What are our options? We've tried to get her to sign over her rights so that she won't have to pay, but she won't. We're being told we can't sue because she doesn't owe enough. What can we do? That back-support sure would be helpful these days.