The antebellum south included the colonial period, and at the time of the American revolution, Virginia had already had slaves for about 150 years. Besides, even after America became independent, in a lot of cases, the old colonial law stayed intact. In fact, the 1705 Virginia slave code I cited remained Virginia slaverly law until 1819
It’s relevant because the act I cited made illegal the importation of all slaves.
First, because the hypothetical women were white, without any “Negro” blood in them, and as far as I can tell, slavery of whites (not counting, of course, those people who we probably would consider white, but were considered “mulattos” at the time) was illegal in every state, north and south, and second, because the act I mentioned earlier banned the importation of slaves, even for personal use, from another country. The Fugitive Slave Act, in both versions, applied to those who were legally slaves in a US state or territory, and not those who may have been slaves in some other country.