Born in Rochford, Judd, who has studied at Castle View School, broke the British under-15 1500 metres record in July 2009, running 4:21.03. In 2011, she added two national under-17 records, with 9:08.5 for the 3000 metres in April and 4:14.21 for the 1500 m in May. Later that year at the World Youth Championships, she won a bronze medal in the 800 metres, with a time of 2:03.43. Also in 2011, she won her third consecutive 1500 m English Schools title. Judd won a gold medal as a member of the British junior women's team at the 2012 European Cross Country Championships. She began the outdoor season by running 2:01.09 for 800 m in a BMC event. At the British Olympic trials in June, she finished third, ahead of UK number one Marilyn Okoro. Then in July at the 2012 World Junior Championships, she won a silver medal in the 800 m final in 2:00.96, which is a UK age 17 record. She went on to reach the 1500 m final, finishing fifth and smashing her previous personal best, with a time of 4:09.93 which is another UK age 17 best. On 22 June 2013, Judd won the 800 m at the European Team Championships. She followed this up with victory at the Birmingham Grand Prix on 30 June 2013, running under two minutes for the first time in her career with 1:59.86. At the 2013 UK World Championship trials, she finished second to Marilyn Okoro, earning selection for the 2013 World Championships in Moscow, where she was eliminated in the heats, running 2:01.48. In May 2014, Judd led the Prefontaine Classic800 metres as a season opener. In June 2014, Judd improved her 800 m best to 1:59.77 in Oslo. In August, at the 2014 Commonwealth Games in Glasgow, she reached the 800 m final, finishing fourth in 2:01.91. Two weeks later at the European Championships in Zürich, she again reached the final, finishing seventh in 2:01.65. In March 2017 Judd won the British Inter Counties Ladies' Cross Country Championships held at Loughborough, earning selection for the British team competing in the World Cross Country Championships later that month in Kampala. On 5 April 2017, Judd ran 8:52.16 for 3000 metres in Watford, to become only the fourth British woman to have broken two minutes for 800m and nine minutes for 3000m, after Christina Boxer, Kirsty Wade and Hannah England. A month later, again in Watford, she improved her 1500m best to 4:05.20.
