Emma lives with her parents in the 1860 and 1870 Census. Her mother dies when Emma is about 16 and her father about 3 years later. Emma may or may not have already married by that time. In any event, by 1880, I cannot find any trace of Emma J Mertz. I checked both Ohio (maybe she lived briefly with one of her uncles) and Pennsylvania and could spot no potentially interesting leads.

It wasn't until researching the attendees at the 1890 Hilbish reunion and encountering the Tool family and then finding the 1900 Census with Emma J Tool born about 1858 that locked it together.

The History of Susquehanna and Juniata Valleys says that Miss Jennie Mertz, youngest daughter of the late P P Mertz, had married a doctor who I assume is a reference to Edward Tool.