Conversation so far:
What is an interesting fact about Tu youyou's background?
Tu youyou studied at the Department of Pharmaceutical Sciences, and graduated in 1955.
What did Tu Youyou discover in her studies?
Tu youyou discovered artemisinin and dihydroartemisinin, used to treat malaria, a breakthrough in twentieth-century tropical medicine
Did Tu youyou work with any others?
Tu youyou was appointed head of the Project 523 research group at her institute. Tu was initially sent to Hainan where she studied patients who had been infected with malaria
Was malaria a problem in China?
malaria was a major cause of death in China's southern provinces, including Hainan, Yunnan, Guangxi, and Guangdong

Question: WHat did she observe?
Self-contained rewrite: WHat did Tu youyou observe?