I don't think it matters for our present purposes where in the world was Mauritania. The big deal is the linking of Juba II, Herod the Great, and Phraates IV, and that all of the areas controlled by that triple-king were nominally under the pale of Rome. All three thrones would probably also have been considered "rump kingdoms" as far as Rome was concerned. The fact that they were broken up geographically was no mistake. Herod was not given Egypt (although he probably had some holdings there), even if he was the Ptolemaic heir.
Prior to Herod there was a King of Cyrene called Magas, a name we might think would belong to Babylon, but he married the daughter of Antiochus I. So, why should it be so surprising that the princess Glaphyra moved between the court of Mauritania, Cappadocia/Pontus, Israel, and even Parthia. We have every reason to believe all of these areas were connected politically.
And all the evidence also suggests that the Ptolemies were striving to fulfill the old pharaonic ideal of being the masters of the known world. The Seleucids no doubt intended to ultimately own Egypt and reconsolidate the "four quarters" from their own vantage point. Not much had changed in the royal mentality since the days of Ramses II or even Thutmose III. In a sense the Herodians achieved that "Great King" ideal, not as Greeks but as part of the Roman royal family.
© Charles N. Pope, US Library of Congress. All rights reserved.