User blog comment:Miskos3/Fairy Tail Chapter 385: The Celestial King vs. the Underworld King, Review/@comment-24734283-20140523231005/@comment-184.3.69.117-20140524005521

Its not about how many keys she got, its the amount of magic power she possesses. Celestial Spirit Mages need their magic power to summon their spirits; especially when it comes to multiple summoning. Like Karen tried to do but failed due to the fact of not having enough magic power to make it happen; and also her body couldn't take it while Lucy's can.