Lloyd, you did not show your sources, so I'm wondering in what context Isabella Hart was identified as a Jew.
Probably the best source of the genealogy of American colonial-era Jews is First American Jewish Families by Malcolm H. Stern. This is a book of 600 genealogies that spans the years 1654 to 1977.Isabella Hart, born about 1680 in Surry County, Virginia, does not appear in the book.
Among online sources, however, there is conclusive evidence of Isabella Hart (visible on ancestry.com).The Douglas Family Tree shows Hester Isabella Hart, with the same birth and death dates and places you stated, and also as the wife of Mark Anthony, born 1650.The family tree shows that Hester Isabella Hart was the daughter of Susanna Rush and John Hart.John (born 1651 in England, died 1714 in Pennsylvania) was the son of Mary Beckley and Christopher Hart. Christopher was the son of John, whose father also was John and whose father was Christopher, the son of yet another John, the son of Henry William Hart (1479-1553). The line of ancestry goes back to John Hart II (1430-1490).
Keep in mind that in 1290, King Edward I expelled all Jews from England.It was not until 1657, under the rule of Oliver Cromwell, that Jews were readmitted.The Hart family of your Isabella lived in England continuously from at least the early 1400s.
Hart is a common name among Sephardic Jews, but, Hart is, after all, an English name and most of the people who bear that name haven't a drop of Jewish blood in their veins.
Based on the names of of the paternal and maternal ancestors of Hester Isabella Hart (1680-1733) that appear in the Douglas family tree, I would state with complete confidence that she was not Jewish.