She is voiced by Marisa Tomei.
Bree herself isn't seen until midway through the film, after Eliza jumps from a moving train after she and Darwin returned to Africa from England to save a Rhino that had been shot. She was posing as a Wildlife Veterinarian. When the Rhino is taken by the Wildlife Rangers, she and Sloan offer Eliza a lift to her parents campsite, but is relieved when she declines. Eliza, Darwin and Donnie later ran into Bree and Sloan yet again at their camp, and the two allowed the group to stay with them for the night.
However, when Eliza discovered Bree and Sloan's poacher equipment in their RV along with a captive Tally, Bree and Sloan's evil true colors were revealed, and they took Eliza and her friends captive. Sloan was fearful about Eliza's mysterious pre-knowledge of the poachers' "fence" in Timbo Valley (actually obtained via Eliza's power to talk to animals) and what else she could know that could threaten Sloan's poaching operation. Before Sloan could interrogate Eliza on what else she knew, Debbie arrived looking for Eliza. Sloan threatened to kill Debbie if Eliza didn't reveal how she knew this (while Bree just tells Sloan to kill Debbie anyway) forcing Eliza to reveal the truth about her power and lose it as a consequence. The resulting supernatural storm that started up as Eliza's power was taken back prompted Sloan and Bree to leave the Thornberrys behind and flee by chopper.
Later that day, as the poachers prepared at Timbo Valley to use bombs to drive the arriving elephants to stampede into their electrified fence, Sloan oversaw and the operation and gave the orders from his and Bree's helicopter. They almost succeeded in murdering all the elephants, but their plot was foiled when Eliza managed to stop the elephants and turn them around just before they reached the fence. Enraged at Eliza's heroic interference, Sloan forcefully picked her up on the chopper's ladder and hurled her into a waterfall. Bree and Sloan then tried to shoot the elephants down from in the air as a backup plan, but the elephants pulled their chopper down out of the air by its ladder and destroyed it. Once the eclipse ended, Bree and Sloan were defeated and cornered by the vengeful elephants and arrested by the rangers.
Bree and Sloan initially appeared as a friendly, warm, charming, and kindhearted couple of animal-loving zoologists, before they were revealed to (in fact) be cruel, greedy, threatening, destructive, murderous, sneaky, evil, and ruthless poachers and the ones responsible for kidnapping Tally. Bree and Sloan were also prominently behind a poacher plot to take advantage of the migration of a thousand elephants to Timbo Valley during a solar eclipse to massacre the elephants by driving them into an electric fence for their ivory.
Although her true colors are not revealed until near the climax, she is one of the main antagonists, because she and Sloan had bigger plans than anyone else. Plus, she and Sloan were thought to be friends to Eliza, but are actually against her.