Sylvia captained the Mt Albert Grammar 1st XV team who won the College Sport Auckland Championship, and was a member of the Ponsonby Senior Women's team that won the 2020 Coleman Shield. In the same year she debuted for the Auckland Storm. An impressive midfielder, Brunt plays for the Auckland Storm and the Blues in Sky Super Rugby Aupiki. 

Sylvia was the youngest Black Fern in the the NZ team that won the Rugby World Cup in 2022. In 2024 she was named as a midfielder in the World Rugby Women's 15s Dream Team of the Year by World Rugby.

In 2025, she was also awarded Pasifika Women’s Breakthrough Player of the Year at the Pasifika Hall of Fame awards.