The death came in an overheated venue in Rio de Janeiro during which Swift, as seen in videos on social media, tried to help thirsty fans by dispatching aides to pass out water bottles and even throwing one to the audience herself.
"Ana Benevides, (who) attended last night's show in Rio for The Eras Tour has passed away," Swift said in a post to her millions of social media followers.
"I can't even tell you how devastated I am by this," Swift added on Instagram.
The Rio Health Secretariat reported that Benevides died Friday after saying she felt poorly and then suffered a cardiorespiratory arrest in the Nilton Santos stadium during Swift's concert, her first in Brazil.
It said efforts to revive the young woman failed, adding that it was too soon to determine "the precise cause of death, which will be investigated."
The death occurred as much of central and southeast Brazil has been suffering an unusually oppressive springtime heat wave.
The heat index in Rio -- combining air temperature and humidity -- had risen as high as 59 degrees centigrade (138 Fahrenheit) during the day.
Event organizers are facing scathing criticism after refusing to allow people to bring water bottles into the venue, despite the soaring temperatures.
Justice Minister Flavio Dion said Saturday that his ministry would adopt "necessary measures on access to water in shows and other public spectacles," as well as investigating responsibility for damage "already caused."
"It is unacceptable that people suffer, faint and even die due to lack of access to water," he said, while adding that the cause of Benevides' death had yet to be formally ascertained.
