Lady Luck is a westernized expression of the Roman goddess
of luck,
Fortuna ( Fortuna is nearly identical to the
Greek goddess Tyche.) Fortuna was the goddess of (good or bad).fortune and luck (good or bad) in Roman religion.
Fortune's decisions in whether to provide good or bad luck in any given situation was a casting of lots (i.e.
a gamble.) She might bring good or bad luck, who knows except the lot in her hand where it will land? Fortune was not percejved by the Romans as literally blind (for she must read the lot), her blindness was a metaphor... she herself did not know what fate she would make. Her predictions were built on
whimsy. Yet in sculptures she sometimes was presented as blind or with a blindfold... as exemplified in contemporary depictions of Lady Justice.
Thus, the terminology "Lady Luck" refers primarily to the concept of not having certainty in a particular outcome, for Lady Luck (i.e. Fortuna) has already picked up another lot to be cast!