In 2006, aged just 14 and while still a second year student, O'Byrne was the youngest member of the Mount Mercy team that won the Munster Senior Schools Cup and the Kate Russell All-Ireland Schoolgirls Championships.

She was encouraged to play for the club by Cliodhna Sargent, an Ireland women's field hockey international and former Mount Mercy student.

[11][12][13] She was again captain when Harlequins finished as runners up in both the Women's Irish Hockey League and the EY Champions Trophy in 2017–18.

[6] She has captained the CIT ladies field hockey team in the intervarsity tournament, the Chilean Cup.

[2][4][7] O'Byrne was a member of the Ireland team that won the 2015 Women's EuroHockey Championship II, defeating the Czech Republic 5–0 in the final.

[19] In January 2017 she was also a member of the Ireland team that won a 2016–17 Women's FIH Hockey World League Round 2 tournament in Kuala Lumpur, defeating Malaysia 3–0 in the final.

[20] O'Byrne represented Ireland at the 2018 Women's Hockey World Cup and was a prominent member of the team that won the silver medal.