i find that through an agency you need to pay 8000 reals ...and then the salary needs to be above 1000 per month... -
you need to provide her with a decent room and i advise that you have a small fridge freezer ther for her own food too...
you will need to provide the basics - one day off a week .... and then a ticked home every 2 years....

through an agency the only benefit from what i can see is really the fact that if it doesnt work out they will arrange for another maid to start straight away and replace this one - so you have insurances like that sort of speak by going with an agency.

if its a private hire then there is visa transfer which could cost 1700 - 5000 reals to transfer her visa from the existing family over to your family ... plus salary ...
this way takes longer to find but in my opinion a bit more worth not so costly ..

good luck