[11] While attending Omagh Academy, McCay was encouraged to play field hockey by her PE teacher, Mary Swann.

[19] After the Elks were relegated from the Women's Irish Hockey League at the end of the 2016–17 season, McCay switched to Pegasus.

[5][29][30] In March 2015 McCay was a member of the Ireland team that won a 2014–15 Women's FIH Hockey World League Round 2 tournament hosted in Dublin, defeating Canada in the final after a penalty shoot-out.

[31][32] On 11 June 2015 McCay made her 200th senior Ireland appearance at the 2014–15 Women's FIH Hockey World League Semifinals in a game against Germany.

As a result, she became Ireland's most capped women's field hockey international, moving one ahead of Nikki Symmons.

[2] 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][36][37] McCay represented Ireland at the 2018 Women's Hockey World Cup and was a prominent member of the team that won the silver medal.

[52] McCay was appointed Member of the Order of the British Empire (MBE) in the 2022 Birthday Honours for services to hockey and to the community in Northern Ireland.