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.
Medical Definition of Bubonic plague. Bubonic plague: An infectious disease that is caused by the bacterium Yersinia pestis and is transmitted to humans from infected rats by the oriental rat flea. It is named for the characteristic feature of buboes (painfully enlarged lymph nodes) in the groin, armpits, neck, and elsewhere.