Kellie won a silver medal in the light welterweight at the 2016 World Championship and then really blossomed by moving down to 60kg. She became world champion in New Delhi in 2018 and also won a bronze at European Championships that year. In 2019 she won silver at the European Games in Minsk but suffered a hand injury in that semi-final, forced her out of the subsequent Europeans. She returned to competition, for the first time in seven months, at the 2020 Strandja tournament in Bulgaria where she lost the final to Mira Potkonen. In 2021 she won another silver at Strandja and she won gold at the final Olympic qualifying event in Paris in June, where her quarter-final defeat of IBF super-featherweight world champion Maiva Hamadouche clinched her Olympic spot.