<<I think the correct reading is the second sentence is "[Had she been]
[a]lone, unable to move, delirious, in pain, 1808 wouldn't have
lasted two days in the African bush, much less the length of time her
skeleton told us she had lived. Someone else brought her water...
Had she been alone, she would have died or more likely been killed quickly.
She didn't, and the most reasonable explanation is that someone protected
her and cared for her.>>
This is my simple point: Why do you assume that 1808 was not among the herd?
IOW, why do you assume she was "alone" save for her supposed nurse (which now
makes her un-alone)?
You are, I think, making the same assumptions the writers make. That's OK, but
they ought to be labeled assumptions.
Jim