She had played rugby league since she was a 5-year old child and only played rugby sevens for the first time at high school.[2] She also played touch football growing up.[3] Southwell said she was inspired by the Australian gold medal winning rugby sevens team at the 2016 Olympic Games.[4]
In 2020, Southwell made history by becoming the first female player to sign a contract with the Newcastle Knights.[6] In November 2021, she was announced as a development player for the Knights' NRL Women's Premiership side.
In August, she officially joined the Knights' NRLW top 24-squad after gaining an exemption from the NRL due to being underage.[5] In round 1 of the 2022 NRLW season, she made her NRLW debut for the Knights against the Brisbane Broncos,[13] scoring a try in the Knights' 32-14 win.[14]
On 2 October, Southwell played in the Knights' 2022 NRLW Grand Final win over the Parramatta Eels, scoring a try and kicking a goal in the Knights' 32-12 victory.[15]
2023
In April, Southwell re-signed with the Knights on a contract until the end of 2027.[16]