Coincidences do happen -
Dana (DAHna) is frequently used in South
Africa as a nn for
Daniel, for instance.
I knew a Derryn (f) who was a 70s baby, but that's as close as it gets. Was there perhaps a celeb or media stimulus leading to the fem use of
Dara back then, do you know? Or even a simple wish to find a name close to but not identical with
Cara?