Yesterday - the Sunday Obituaries - I included Agnes' Death Announcement. It was from the Village Record 13 March 1860 and read "In East Fallowfield, on the 24th ult, Mrs. Agnes Still, wife of David Still, aged 41 years and 1 month."
Agnes (nee Armstrong) died at the age of 41 in February due to pleurisy, which she had for one week. This is according to "Schedule 3 - Persons who dies in the year ending 1st June 1860 in East Fallowfield Township in the County of Chester State of Pennsylvania." According to the Mayo Clinic, pluerisy is "when the double membrane (pleura) that lines the inside of your chest cavity and surrounds each of your lungs becomes inflamed." She is buried at Hephzibah.
Agnes Armstrong and David Still were married by Rev. J. Hand on 18 February 1845, according to their marriage announcement. The two had one child: William. David remarried after her death.