The amazing thing about this story is that the girl lives with her mother, not him. And the girl is 18 going on 19, so she's an adult. And the girl has a child to raise, so I'm thinking being a mom is probably a priority before passing math.
I agree that she should be legally required to get her GED. If I had my way, every teen age mom would be required to get a GED just so they can provide a better future for their child. But I wouldn't put her dad in jail and make her dad risking losing his job to do it. Would you?