Nielsen won the 400 m hurdles at the
2021 European Athletics Team Championships with 55.59. Nielsen has a twin sister,
Laviai Nielsen, who is also an international athlete over 400m. At the
2024 World Athletics Indoor Championships in
Glasgow, Nielsen won a bronze medal as part of the 4×400 metres relay team, which also included her sister Laviai Nielsen. After becoming the
British 400 metres hurdles champion at the
2024 British Athletics Championships, Nielsen was subsequently named in the
Great Britain team for the
2024 Summer Olympics where she went out in the semi-finals after hitting a hurdle and falling to the track. Recovering from that setback, Nielsen ran for Great Britain in the heat of the women's 4×400 metre relay, qualifying for the final in second place. Although, like her three fellow heat runners, she did not run the final, the third place finish for the Great Britain team in that final confirmed that Nielsen had won her first Olympic medal, a bronze. On 15 February 2025, she broke the British women’s indoor 300m record in a time of 36.53 seconds in Birmingham. At the
2025 European Athletics Indoor Championships in
Apeldoorn, she was part of the British 4×400 metres relay team which won a silver medal. Nielsen retained her 400 metres hurdles title by winning the
2025 UK Athletics Championships.
Athletics achievements International competitions Circuit performances == Personal life ==