This lady is in her 60s, does she even know any other way to even live? Life with that family may be better than whatever Brazil's equivalent of welfare shelters are.
Seems like that may have been why the case workers left her with that family for now.
This can result in them being exploited again by even more unscrupulous people. The articles clearly mentioned how difficult these cases are to deal with. While they do not go into detail, the above is why.
Its very easy to gain peoples trust when they have no sense of normal anymore, and can you sign this paper, o, we need to go to a friendly notary to help with it. and before you know it, the people just handed over their apartment / or whatever.
There are a lot of good people with will want to help but it only takes one rotten apple to destroy peoples live again. Recently in Europe there was a case of a helper that took elderly their IDs and helped herself to their money. She made 100s of victims. Now imaging that type of person with somebody who probably did not have any proper education and normal independent life experiences that we all had the luxury of having.
In a ideal world, we have proper state funded solutions, with proper oversight to help people integrate into society. Reality is that if any services exist, they are underfunded, often lacking oversight and people fall into the often chasm of cracks.
These type of stories are never clean white and black, but a mix of gray sludge, where we all hope for the perfect ideal solution but often there are not many options. And naivety tend to often do more harm then good.