Simm made her international debut in 2010, at a friendly meet against Australia, where she won gold on vault and bronze on floor exercise.
Simm made her senior debut at the British School Games, winning silver in the all-around. She went on to compete at the Rushmoor Rosebowl, winning bronze in the all-around, on vault, and balance beam.
At the English Championships in 2012, she won silver on vault and placed fifth on floor. She went on to win team bronze in two friendly meets, one against Switzerland, the other against Germany. At the British Championships, she won vault bronze and placing fifth on floor. She returned to the Rushmoor Rosebowl, winning balance beam gold, and vault silver. She went on to compete at another friendly meet, this time against Germany and Romania, winning team bronze and placing tenth in the all-around. She was not named to the British team for the Olympics in London, but continued to compete afterwards. At the end of the year, she competed at the Voronin Cup in Russia, placing fourth on vault, fifth on bars and floor, and seventh with her team, in the all-around, and on balance beam.
At the British Championships, she won silver on vault and placed seventh in the all-around, bars, and beam, and went on to finish seventh at the British Team Championships. In late summer, she competed at the Turnen Dames Interland in the Netherlands, winning vault bronze, and placing sixth on floor and eighth in the all-around. In the fall, she competed at the Elite Gym Massilia in France, winning team bronze, and placing sixth on vault and fourteenth in the all-around. She returned to France in December for the Pas de Calais Internationals, winning team gold, vault and bars silver, and all-around bronze.
At the English Championships, she won floor exercise gold, all-around silver, vault bronze, and placed fifth on bars and beam. At the British Championships, she claimed her first National title on vault, and placed sixth in the all-around and on balance beam. She competed at a friendly meet in Munich against Germany and Spain, winning team gold and placing fourth in the all-around.
Although she didn't compete at the European Championships, she was named to the English team for the Commonwealth Games, winning gold with her team and placing fifth on vault. In September, she competed at the British Team Championships, and although her club finished in eighth place, Simm had the highest all-around total of the competition, and was promptly named to the British team for the World Championships. There, she helped the British team qualify for the team final in fourth place (their highest placement in qualifications), though they finished sixth in the final.
Simm competed at the English Championships in March, winning floor gold, vault silver, all-around bronze, and placing fifth on bars and sixth on beam. At the British Championships, she won silver on vault and placed fourth in the all-around and on floor. In late May, she placed fifth with her team at the Flanders International Team Challenge in Ghent, Belgium.
Simm was named to the British team for the inaugural European Games in Baku in June. She helped the British team to an eighth place finish and placed eleventh in the all-around. However, she finished last in the vault final after receiving a zero on her second vault when she didn't land feet first.
Simm improved greatly at the Universiade in South Korea in July. She won all-around gold, vault silver, floor exercise bronze, and placed fourth on bars. Simm became the first British gymnast to win the all-around at the Universiade. In October, Simm was named to the World Championship Team. In Glasgow, she helped the British team qualify third to the team final and qualify a full team to the Olympics. She didn't compete in the team final, but she stood with the team when they accepted a historic bronze medal, their first team medal at the World Championships. She also submitted a new release move on uneven bars to the FIG: a piked Stalder Tkatchev. However, since German gymnast Sophie Scheder submitted the same skill and both gymnasts successfully performed it, neither got the skill named after them.
Simm started off the season at the British Championships, placing fifth on uneven bars, balance beam, and floor exercise, and sixth in the all-around. She did not make the Olympic team, but continued to compete after Rio, placing seventh on bars at the Varna World Cup in Bulgaria in September. In October, she placed fifth on bars at the Cottbus World Cup in Germany.
Simm started the season at the English Championships in February, winning bronze on uneven bars and placing fourth in the all-around and on floor exercise and seventh on balance beam. In March, she competed at the American Cup, hitting four clean routines to finish fifth in the all-around. A week later, she became British National Champion, and won an additional gold medal on uneven bars and bronze medal on floor exercise.
In April, Simm returned to the Commonwealth Games. She helped the English team take silver, and individually won bronze on balance beam and placed fifth in the all-around and on uneven bars. She went on to compete at the Thialf Summer Challenge in July, winning team bronze and placing fifth in the all-around. In August, she competed at the European Championships in Glasgow, Scotland, placing fourth with her team and eighth on uneven bars. She was named to the British team for the World Championships in Doha, Qatar in late October. Great Britain didn't make the team final, but Simm qualified to the all-around and finished nineteenth. After Doha, she competed at the Cottbus World Cup in November, placing fifth on bars.
Simm returned to the English Championships in early March, winning all-around and uneven bars silver, floor exercise bronze, and placing ninth on balance beam.
2018 - "Catgroove" by Parov Stelar/ "Clash" by Caravan Palace/ "Delight" by Jamie Berry