User blog comment:FairyRaven/Fairy Tail Chapter 465: 400 Years, Review and Commentary/@comment-25334245-20151207125618/@comment-49.148.13.104-20151207143607

During the Grand Magic Games, remember Arcadios saying that the life of a Celestial Spirit Wizard will be sacrificed in order to open the Eclipse Door. That's why the planned to kidnap Lucy. But, when they saw that the 12 keys are complete, they changed the plan and a life is no longer to be sacrificed. They just arrested Lucy and Yukino tob get all the 12 keys.

This means Layla doesn't have all 12 keys. That's why she sacrificed her life to open the Eclipse Gate in order to defeat Zeref.