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.
Bubonic plague is the most common form of plague, an illness that occurs in humans, rodents, and ectoparasites (fleas and lice). The condition is caused by Yersinia pestis bacteria and characterized by large, infected lymph nodes called buboes.