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 an infectious disease caused by the bacteria known as Yersinia pestis. Plague has a high fatality rate and has been described for centuries. In the Middle Ages, plague was known as the Black Death and caused the death of 60% of the population of Europe. Transmission occurs via fleas that feed on infected animals, typically wild rodents. There are three forms of plague in humans: bubonic plague, septicemic plague, and pneumonic plague.