Joh. Georg Harter m. Eva Bracker
I finally found it! In the records of St. Paul's Evangelical Lutheran Congregation, LeHigh County, PA. is found:
Oct 26, 1752George Herder m. Eva Bracker, Christian Bracker's daughter.
This at last puts to rest the maiden name of Eva. Not only that, but according to "Pennsylvania Births, Lehigh County, 1734-1800" these church records also record the birth of Georg and Eva's oldest son, Joh. Christian, as occurring 4 Aug 1753. I have seriously doubted the commonly found birth location of their children as being Bedford County. Christian, at least is now known to have been born in Lehigh County. I could not find any record of other children's birth, so assume the family moved. I have reason to believe they may have been in Berks County, but so far have no proof of this. It would be logical, however, because Berks is between Lehigh County and Frederick County, MD, where they appeared in 1769.