User blog comment:Wrath022/Chapter 516: The Truth About Enchantment, Review/@comment-24277053-20161227034433/@comment-1776824-20161227040037

Apparently because Irene is a dragon enchantress and Wendy is a dragon slayer enchantress (Wendy has the dragon seed), Irene can enchant her mind over Wendy's. Even though Erza is flesh and blood, it is impossible to do so. For some reason.