User blog comment:B214/Volume 23 discussion blog/@comment-31137559-20170307010853/@comment-9595671-20170307163421

Elmenhilde did have a kid with Issei in the EX novel, so it's already been confirmed, we just don't know how she ends up in Issei's just yet.

Kinda like how we count Kunou in the harem for moving into the Hyoudou household but we've yet to see her kid in EX, to be fair she's young right now, so her kid might have been too young to help like Le Fay's, hence why we didn't see it.