User blog comment:LastationLover5000/Speculation Time With Ahatake (Fairy Tail 297)/@comment-3061966-20120901014645

Oh boy, it's fan theory time.

Can't be Layla, she has no reason to cry over seeing Natsu.

I think the Future Lucy idea is plausible.

I saw something interesting on another forum that supports the Future Lucy thing:

"It was mentioned in Mashima's drafts that Lucy would be kidnapped by Zeref and that she was told that she would never see Natsu again. I'm pretty sure the mysterious girl is Future Lucy and the reason she cried when she saw Natsu was because she was finally seeing him again after a long time. It wouldn't make sense for anyone else to cry at seeing Natsu except for Zeref or Lucy, and it's not Zeref. As for why this Future Lucy has Zeref's magic, maybe she was forced to learn it, or perhaps she mastered Toki no Arc (Lost Magic connected to Zeref) in order to travel back in time to warn everyone of the upcoming apocalypse."

What hurts the Lucy theory is that the woman has showed up a number of times over the years to the tournament.