Hmm. Not sure it's fair to use the word "fair" regarding any relationship between a slaveholder and an enslaved woman. It could never have been an equal relationship because Sally had no real agency--and therefore inherently unfair and imbalanced.
Yes, she could have remained in France, but as you point out, her family was back home. And she was pregnant. Then, there is the question of sexual grooming from an early age. Thorny stuff, all, even though their intimate relations may have been loving in nature, it's hard to get the "ick" out of this story.
Still, you've offered plenty to think about. And I really appreciate the wonderful source materials you included.
BTW, Jefferson's use of Callender to attack Hamilton came back to bite him later. Reminds me of more recent history and how the "dirt" dug up by one party during the primaries was put to use by the other party during the general election. Hard to put that monster back in the box!