User blog comment:IamJakuhoRaikoben/Chapter 497: The Winter Mage, Review./@comment-184.178.44.233-20160810195824

Perhaps the reason that Irene is so strong (this is relatively speaking) is because of some family power that was passed down to her. I think that Irene and Erza are sisters. The Berselsion family perhaps noticed that Erza had more potential than Irene and was gonna give her the power of the Berselion family. Irene got jealous because she is supposed to be the elder sister and should inherit their family's power, that's why she betrayed Erza and left her at Rosemary Village so that she'll inherit the familial power. She probably annihilated everybody in the Berselion family as a revenge. Neinhart can be also be a descendant or at least affiliated with the Berselion family. The way he addressed Erza - as Lady Erza - seems to hint that.