User blog comment:FairyRaven/Fairy Tail Chapter 377, 378: The Sky Dragon's Rage & Friends Forever, Review and Commentary/@comment-37.236.184.55-20140328112853/@comment-7418318-20140328113441

She was already able to control her ability shortly after returning from Edolas, when she predicted a conversation and it's content between Macao and Wakabe, but that control was then messed up by the time-skip. It's only natural that the control would return sooner or later.

On Tenroujima all her predictions were right. She foresaw danger and she foresaw some people crying. All of that turned out true. And in the GMG arc she had one wrong and one true prediction. The "White Knight" really appeared, but Mercurius did not collapse with Lucy crying in the ruins.