You say that Emmarentia was "presumably" named after such a woman, but is there real historical evidence for that? Emmarentia looks to me to be simply a respelling of Emerentia, the name of an early
Christian martyr in Rome. This becomes Emerenzia in modern Italian, Emerencia in Spanish, and Emerence in French. Indeed, my Dutch name dictionary (
Woordenboek van Voornamen by van der Schaar) gives Emmarentia as one of several spellings of this name that has been used in the Netherlands. So it seems likely to me that the town in South
Africa was named after a woman whose full given name was Emmarentia, and that the idea that it's named after an "
Emma Rens" is a folk etymology developed after Emmarentia had become unknown as a given name in the area.