Brazil outshot Mexico 25-3 with the CONCACAF side unable to manage one on goal throughout.
Second-half substitute Byanca broke the deadlock taking a short ball from the right, using a touch to get to the edge of the restraining arc and unleashing a curling left-footed drive that arched over diving Mexican keeper Gabriel Paz.
Mexico remained in second place in the group with three points, just behind Japan - which played New Zealand later Wednesday - and just ahead of Brazil on goal difference.
But Mexico must face Japan in its group finale on Sunday, while Brazil will play New Zealand.
Brazil dominated the first half but produced few quality chances, but was able to intensify its effort after halftime, hitting the post with a shot by Djenifer in the 54th minute.
Byanca entered the match in the 69th minute for Brena and tallied her winner 13 minutes later.