I think you can sell yourself into slavery; I could see many poor people having to do that as their last chance to avoid starving (for them and their family).

That, or the too poor to function option; I can see this government choosing slavery to deal with poor people, exactly like they do with (most) criminals.

So maybe Juana's daughter was enslaved as well. But maybe she'll appear as a free person, when she does. She got freed somehow, and maybe she went looking for her mother, but she'd changed owner since then and was nowhere to be found. (In Fisk's home.)