User blog comment:Ncduru/The Erza-Irene Connection/@comment-207.45.155.253-20160425130814

She's likely the mother I think. Perhaps she had Erza at a really young age, hated herself for getting pregnant, and decided to leave Ishgar for Alvarez to start a new life. Neinhart and Brandish looks to be about the same age, and Neinhart addresses Eileen as "Lady" Eileen, which is how they address older people (relative to themselves).