That Eileen lady might be her other. just a guess.
i'm more agree if Eileen lady erza's relative, cause erza since child never use magic till heaven tower. and then she go to fairytail (almost impossible magician in other continent know her). and i think Eileen lady nice person, but have strong magic. her position maybe like lucy mom. great magician that feared, or ul.
Maybe its Erza's sibling or Mother? It could even be her Auntie, Cousin and Grandmother haha. Okay I'm just prolonging what you said about "relatives". so yeah, maybe its one of her relatives :)
*mother
Yess i think it may be her mother but we don't know anything at all about her whole family so it can be her sister or something like that too. We'll have to wait to know.. but she will be veeeery strong for sure haha
I Just Hope That This Eileen Person Will Become Their Ally, Like If She Saw Erza, She Might Turnover To Their Side And Protect Her.
Oh fuck, if that Eileen person is Erza's relative and is with the bad guys, Fairy Tail problems are raising (￣∇￣")