How Leah arrived on the island is an enigma. In all probability, Leah most likely slipped into a strange Gate or temporal distortion in the years before 65000000 B.C. The veracity of her status as Ayla's mother is debatable, but it is possible that Mystic Mountains of Prehistory was temporally active (Kino also strangely appeared there one day). The Gate took her to Gaea's Navel (which existed even before Chronopolis terraformed El Nido, which provides for her ability to return and mother Ayla before El Nido would have been created). She then presumably returned the way she came after Chrono Cross concluded.