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: A deadly bacterial disease of the lymphatic system,often marked by buboes, which are visibly swollen lymph nodes. Be-cause buboes and other parts of the body often take on a dark cast, theplague came to be called the Black Plague or Black Death.