Police in Changsha, capital of Hunan, said that the woman surnamed Ouyang had been arrested for her role in the assault that happened at early on Monday.
Victims of the violence were a female doctor and a nurse five months into pregnancy. Their hospital, the First Hospital of Hunan University of Chinese Medicine, said the doctor suffered bruises and concussion, and the nurse reported signs of threatened miscarriage.
Police said Ouyang and other relatives of a lung cancer patient beat the doctor and the nurse because they were dissatisfied with the emergency treatment.
After the patient died, Ouyang also forced the 29-year-old doctor to kneel before the body for several minutes, state-run Xinhua news agency reported.
Police said that Ouyang was unemployed.
China has seen a spate of attacks on medical staff in recent years amid strained patient-doctor relations. Chinese patients often accuse doctors of rushing consultations and also of prescribing excessive medicines, while doctors have complained about overwork, low pay and being frequently misunderstood.