She joined the Young Communist League at the age of 16 during the 1926 United Kingdom general strike, and soon afterwards was seen chairing meetings with the communist trade union leader Arthur Horner, and later joined the CPGB. Although she was also a member of the UK Labour party, she remained a lifelong member of the CPGB. During her teenage years in Reading, Silverthorne supported herself by selling the "Daily Worker" to railway staff, and she worked as a Nanny for Reading Labour Party MP and founder of the Socialist Medical Association (SMA), Somerville Hastings. Hastings was known to have supported Silverthorne's ambition to become a nurse. In March 1931, Silverthorne started training as a nurse at the Radcliffe Infirmary in Oxford, where her older sister Olive was already working as a nurse. She volunteered as a nurse for Lancashire hunger marchers passing through Oxford during the National Hunger March, and was prone to "helping herself to bandages and dressings" from the wards of the Radcliffe Infirmary. During her time in Oxford, she was given the nickname "Red Silverthorne" for her communist activities, and would also become friends with the Marxist historian Christopher Hill who she met through the Oxford communist society known as the October Club.