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.
The plague is an infectious disease caused by a bacterium called Yersinia pestis that can affect both animals and humans. There have been many outbreaks of plague in human history, which have killed more than 200 million people around the world. Perhaps the most widely known plague is the Black Death of 14th century Europe. This was bubonic plague. Outbreaks of plague are a rare occurrence today.