User blog comment:IamJakuhoRaikoben/Chapter 497: The Winter Mage, Review./@comment-71.120.223.31-20160808175221/@comment-88.145.220.244-20160808180629

i'd imagine that Eileen wants Erza dead for the same reason she joined Zeref, to cut all her ties to ishgar and forget/move on from her painful past; that's my speculation anyway.