O'Flanagan made her senior debut for Ireland in 2012. She subsequently represented Ireland at the 2013 Women's EuroHockey Nations Championship. On 22 July 2017 at the 2016–17 Women's FIH Hockey World League Semifinals, after Ayeisha McFerran was sin-binned in the seventh and eighth place play-off against India, O'Flanagan came on as replacement. With her first touch she saved the subsequent penalty stroke. Ireland were 1–0 down at the time but eventually went onto win 2–1. Ireland's seventh-place finish in at the tournament eventually saw them qualify for the 2018 Women's Hockey World Cup. At the 2017 Women's EuroHockey Nations Championship, O'Flanagan was Ireland's first choice goalkeeper.