Brittany first emerged on the junior scene, representing Australia at junior international meets as a teenager. She made her first senior international team in 2012, as an 18-year-old, when she was selected for multiple Olympic relay squads. In London, she earned a gold medal as part of the 4x100 free team, where she swam finals, and she also earned two silver medals for her prelims swims on the 4x200 free and 4x100 medley relays.
Since competing at the London Olympic Games, Brittany has been a relay fixture for Australia, earning two more Olympic medals, three long course and two short course World Championship medals, two Pan Pacific Championship meals and three Commonwealth Games medals. In 2016, she was named the Sunshine Coast Senior Sports Star.