She was a secretary working at the sheriff's office, when Sam and Dean Winchester were brought in by Victor Henriksen. She was fundamental to concieve a spell suggested by Ruby to destroy attacking demons, due to her being a virgin, however this spell is not performed, and instead the demons are exorcised.
Nancy, the secretary at the sheriff's office that is under siege by Lilith's demons, was a devout Catholic. She responded to Sam's request for a towel after Dean is shot, only to be grabbed by him as he steals her crucifix. Later she helped patch Dean's wound.
Voluntarily celibate, she volunteers herself as the virgin sacrifice in Ruby's suggested plan to perform a spell and destroy the attacking demons. Dean, however, doesn't approve and comes up with an alternate plan that won't require a sacrifice.
Nancy helps during the alternate plan that they go with, and survives the siege, only to be killed by Lilith along with the rest of people in the building shortly after Sam and Dean leave.