User blog comment:Miskos3/Fairy Tail Chapter 385: The Celestial King vs. the Underworld King, Review/@comment-24734283-20140523231005/@comment-7418318-20140524083749

I'm not so sure about the tripple summoning being a bad choice in general. Remember that Lucy was already pretty exhausted from the fights against the smallfry in undercube and from being drained by Franmlath when the final battle started.

It is possible that she can savely summon three Spirits if she's fresh and that Loke and Vigo were underestimating how much she has grown. And there's also the chance that this new gift might increase the total magic power she has available to pull stunts like tirpple summoning.

Of course this is just speculation, but I don't think there's anything to directly contradict the possibilities.