Background: Tu Youyou (Chinese: Tu You You ; pinyin: Tu Youyou; born 30 December 1930) is a Chinese pharmaceutical chemist and educator. She is best known for discovering artemisinin (also known as qinghaosu) and dihydroartemisinin, used to treat malaria, which has saved millions of lives.
Context: Tu Youyou carried on her work in the 1960s and 70s during China's Cultural Revolution, when scientists were denigrated as one of the nine black categories in society according to Maoist theory (or possibly that of the Gang of Four).  In 1967, during the Vietnam War, Ho Chi Minh, the leader of North Vietnam, which was at war against South Vietnam and the United States, asked Chinese Premier Zhou Enlai for help in developing a malaria treatment for his soldiers trooping down the Ho Chi Minh trail, where a majority came down with a form of malaria which is resistant to chloroquine. Because malaria was also a major cause of death in China's southern provinces including Hainan, Yunnan, Guangxi, and Guangdong, Zhou Enlai convinced Mao Zedong to set up a secret drug discovery project, named Project 523 after its starting date, 23 May 1967. Upon joining the project unit, Tu was initially sent to Hainan where she studied patients who had been infected with the disease. During the time she spent there, her husband was banished to the countryside, meaning that her daughter had to be entrusted to a nursery in Beijing.  Scientists worldwide had screened over 240,000 compounds without success. In 1969, Tu Youyou, then 39 years old, had an idea of screening Chinese herbs. She first investigated the Chinese medical classics in history, visiting practitioners of traditional Chinese medicine all over the country on her own. She gathered her findings in a notebook called A Collection of Single Practical Prescriptions for Anti-Malaria. Her notebook summarized 640 prescriptions. Her team also screened over 2,000 traditional Chinese recipes and made 380 herbal extracts, which were tested on mice.  One compound was effective, sweet wormwood (Artemisia annua), which was used for "intermittent fevers," a hallmark of malaria. As Tu also presented at the project seminar, its preparation was described in a 1,600-year-old text, in a recipe titled, "Emergency Prescriptions Kept Up One's Sleeve". At first, it didn't work, because they extracted it with traditional boiling water. Tu Youyou discovered that a low-temperature extraction process could be used to isolate an effective antimalarial substance from the plant; Tu says she was influenced by a traditional Chinese herbal medicine source, The Handbook of Prescriptions for Emergency Treatments, written in 340 by Ge Hong, which states that this herb should be steeped in cold water. This book contained the useful reference to the herb: "A handful of qinghao immersed with two litres of water, wring out the juice and drink it all." After rereading the recipe, Tu realised the hot water had already damaged the active ingredient in the plant; therefore she proposed a method using low-temperature ether to extract the effective compound instead. The animal tests showed it was completely effective in mice and monkeys.  Furthermore, Tu volunteered to be the first human subject. "As head of this research group, I had the responsibility" she said. It was safe, so she conducted successful clinical trials with human patients. Her work was published anonymously in 1977. In 1981, she presented the findings relating to artemisinin at a meeting with the World Health Organization.
Question: What did she discover in her studies?

Answer:
Tu Youyou discovered that a low-temperature extraction process could be used to isolate an effective antimalarial substance from the plant;