User blog comment:IamJakuhoRaikoben/Chapter 468: Memory of the Stars, Review./@comment-27281341-20160109202517/@comment-26167397-20160109214029

I think its b/c you know she was suppose to give it to Lucy when she decides to become a CS mage, and the fact she knew Lucy got it right after Grammi died made her think to get it, she had to kill her.