Since the maiden name of Melissa Davis' mother on her death certificate is considered secondary information, I needed the marriage record to verify that - which it did.
Since FamilySearch has digitized and put online Pennsylvania probate records, I started there, with the probate records for Armstrong County. While there were some wills written by Reynolds men (David, Richard, Absalom and Alexander), none of them named Cassandra. Richard Reynolds had a daughter Evaline, but her married name was Frampton.
I had struck out on Armstrong County, so I took a look at the map of Pennsylvania Counties as they were in 1850, on the Atlas of Historical County Boundaries (http://publications.newberry.org/ahcbp)
The answer to my question was found in an original record that was not on Ancestry. Any genealogist who relies only on Ancestry is really, really missing out.