Unfortunately exchange rates can vary and local fees can vary slightly. The online application should confirm the correct fee if you have applied for the correct visa (I presume adult dependant relative). I would expect an adult dependant relative visa application fee to be 3,145 USD:
She will need to apply in Brazil with the relevant documents and should provide a copy of every original document supplied. It is a good idea for her to travel with the same original documents in hand luggage in case questions are asked although I would not expect her to have any problems.