In 1911, Casson's uncle, Isambard Owen, vice-chancellor at University of Bristol, promised her a place studying medicine if she could be formally matriculated to the university. She struggled with her Latin exams for two years, but eventually passed them and registered to study medicine on 1 October 1913 at the age of 32. She graduated with her Bachelor of Medicine degree in 1919, and took on a role at the West Hertfordshire Hospital in Hemel Hempstead. There she noticed that patients in the women's wards were enjoying using artistic talents, and decided that such pursuits were important to treatment. She realised that these pursuits were not only keeping the patients occupied but also helping them to gain self-esteem and to work through their issues.