On 21 June 2019, she started at second-row for New South Wales under-18 in their 24–4 win over Queensland in the first ever Women's under-18 Origin game. She scored a try and was named Player of the Match.[5][6] In July 2019, Johnston-Green joined the Sydney RoostersNRL Women's Premiership team.
On 22 February 2020, she started at prop for the Indigenous All Stars in their 10–4 win over the Maori All Stars.[10] In March 2020, Johnston-Green joined the Central Coast RoostersNSWRL Women's Premiership team.[11] Johnston-Green suffered a knee injury while playing for the Central Coast and was ruled out of the 2020 NRL Women's season.[12]
On 1 July 2021, Johnston-Green was announced as the Newcastle Knights' first ever NRLW signing.[14] In February 2022, she was announced as one of the club captains.[15]
In late September 2022, Johnston-Green was named in the Dream Team announced by the Rugby League Players Association. The team was selected by the players, who each cast one vote for each position.[17]
On 2 October 2022, Johnston-Green played in the Knights' 32-12 NRLW Grand Final win over the Parramatta Eels.[18]
In 2023, Johnston-Green played at prop in the Knights' 24-18 Grand Final win over the Gold Coast Titans.[19]