she was 5 when she auditioned and 6 during the filming
The published 'log line' for this film, on IMDb reads:
"Faced with both her hot-tempered father's fading health and melting ice-caps that flood her ramshackle bayou community and unleash ancient aurochs, six-year-old Hushpuppy must learn the ways of courage and love."
According to Wikipedia's page about this film:
"The fictional island of the film, "Isle de Charles Doucet" known to its residents as the Bathtub, was inspired by several isolated and independent fishing communities threatened by erosion, hurricanes and rising sea levels in Louisiana's Terrebonne Parish, most notably the rapidly eroding Isle de Jean Charles. It was filmed in Terrebonne Parish town Montegut."
The duration of Beasts of the Southern Wild is 1.53 hours.
Based on its geography, the locale where Hushpuppy lives is sunken and collects water -- hence the name 'bathtub'.
You can review the link, below, which lists accolades for this film.