A long shot, but since you mentioned both KELLER and SCHAEFFER...my gggrandmother was Leah KELLER, b ca 1827, probably in Dauphin Co. She married, ca 1845, William SCHULTZ of Newmanstown, Lebanon Co. They had two children:
Abner William SCHULTZ b 16 Jul 1846
Mary Elizabeth SCHULTZ b 29 Apr 1849 (my ggrandmother).
William SCHULTZ d ca 1849, and in 1852 Leah married John Jacob SCHAEFFER, a stonemason. They lived in Middletown, Dauphin Co (where I think SCHAEFFER was from), and had one daughter that I know of, Anne Elizabeth SCHAEFFER b 1854.
My problem is that I have not been able to find out who Leah's parents were. I have seen that genealogy of KELLERs who married SCHAEFFERs and I can't connect Leah to it, can you? I rather suspect it is a coincidence since neither KELLER nor SCHAEFFER is rare.