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 primarily an infection of animals including many species of rodents (including mice, rats, ground squirrels, prairie dogs, chipmunks and rabbits). In the United States, it is most commonly transmitted to humans by the bite of an infected rat flea (Xenopsylla species).