These random enemies in the 'Omajiki' event...

It's Leafa (ALO) who randomly appears before the Watcher after clearing a stage in this event and challenges you to an 'Omajiki' battle (you can summon her for a forced battle up to 3 times a day). Why does this character keep reviving no matter how much I beat her in the 'Omajiki' battles? For more details, it should be easier to understand if you read volumes 9-14 of the original SAO novels.