There is no way that Sun is the woman who left with Lapidus.
Mea culpa?
Absolutely.
Mea maxima culpa.
But I still think my logic was sound. We are all now left with the question of why Sun didn't flash to 1977 with the others. This will have to be explained, and no doubt will be in future episodes.
My own guess at the moment is that Sun is already there in the 1977 Dharma compound, probably as Pierre Chang's baby or another child in the village. That, of course presumes a time travel "rule" that the same person cannot occupy the same space at two different times.
But we have seen Locke on the Island seeing the hatch light beam in the sky while he was, at that moment in an earlier time, on that very hatch door. And Sawyer observed Kate helping Claire in labor while the Sawyer from that time was somewhere else on the Island.
Maybe the specifics of the rule are that a person cannot physically see, hear, touch, etc. themselves and that there would be too great a danger of that within the close confines of the Dharma village.
As you can see, falling flat on my face doesn't stop me from climbing out on another theoretical ledge. I'm flexible.
