She attended Bishop Bell School and began playing youth football for Eastbourne Borough when she was five years old, before joining Polegate Grasshoppers when she was 11.

She made a promising start, as the club's joint-leading goal scorer for 2014, and extended her contract for another year at the end of the campaign.

Ladies F.C., including during their 2016–17 UEFA Women's Champions League campaign,[2] where she scored both goals in Cardiff's 3–2 loss to Spartak Subotica.

However, due to suffering a fractured tibia against Reading in a pre-season friendly, she missed the entirety of her debut season at the club.

In total, she made eleven appearances that season, being rewarded with three player of the match awards netting her one and only goal against champions Leicester.

[23] On 19 June 2022, Agg made her debut for the Republic of Ireland women's national football team in a friendly against the Philippines in Antalya, Turkey.

[25] Agg had previously represented England up to under-19 level, but changed her allegiance to Ireland after an approach from the team's coach Vera Pauw.

[26] On 1 September 2022 Agg was named player of the match in Ireland's 1–0 2023 FIFA Women's World Cup qualification – UEFA Group A win over Finland at Tallaght Stadium.

She entered play as a first-half substitute for the injured Ruesha Littlejohn then headed the winning goal, which secured Ireland's place in the 2023 FIFA Women's World Cup qualification – UEFA play-offs.