Jefferson’s wife Martha died in 1782 when Sally Hemmings was 9 years old.
I understand; that doesn’t explain hopping in the sack with her half-sister. If my wife passes away, I think I’d be looking outside the pool of in-laws for a mate.
It certainly is a possibility that Jefferson did have relations with her; it is still such a stretch that stating it as fact is revisionist history. As pointed out earlier, it was to justify BJ Clinton’s BJs.