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.
plural plagues. Learner's definition of PLAGUE. 1. [count] old-fashioned : a large number of harmful or annoying things. The country was hit by a plague of natural disasters that year. a plague of locusts. There has been a plague of bank robberies in the area.