The baby was born in the United States but has been living in Brazil for 6 years. The mother is a Brazilian citizen.
Can a woman living in Brazil collect child support from someone in the United States?
Yes. There would need to be first, a legal establishment of paternity if that is not already in place, and then an application to a court for a child support order.
The question of whether one should proceed in a U.S. court or a Brazilian court is a tactical one that would be evaluated based upon the circumstances by the lawyers involved in doing so.
Generally, that would open the door to child custody proceedings as well in the same, or a parallel case.