Multiple realities
(covers information from several alternate timelines)
The name "Molly" was popular among the citizens of Gaia, having been passed down through the O'Brien line. Yedrin Dax explained this to Miles O'Brien when he expressed surprise at hearing Lisa call another girl Molly in 2373.
Later, while speaking to that Molly, Miles told her of his own daughter, also named Molly, her namesake. (DS9: "Children of Time")