The enumeration date is as you surmised the actual date the info was recorded. The official enumeration date was 1 June 1850, all questions were to refer to that date. So she probably died sometime between 1 June and Sept 11. Don.
Definition of plague. 1  an annoyance; those children are a damn plague. 2  any large scale calamity (especially when thought to be sent by God) 3  a swarm of insects that attack plants; a plague of grasshoppers. 4  any epidemic disease with a high death rate.
Plague is a severe disease caused by the bacteria, Yersinia pestis (Yur-sin-EE-ah pes-tis). Many animal species, including humans, can get the disease. Various forms can occur, each with differing symptoms, and possibly death. Outbreaks occur in North and South America, Africa, the Middle East, and parts of Asia.