Board Thread:Spoilers!/@comment-1916997-20170628070859/@comment-25926288-20170628225447

Unknown.

Actress aside, all we know is a possible codename "Carol" and they are casting for an adult female. The lines were likely completely unrelated to her character as it appeared to be taken directly from Hat Trick with a little deviation with names, etc.

So, to recap things with a surety,

1. An adult female

And thus it can be the younger version of the Old Lady who lived in a shoe for all intents and purposes. The Hat Trick use of dialogue is likely just to get her to read lines and audition, nothing else. I doubt the casting director and co. is going through a lot of trouble to specify dialogue of a specific episode that's pretty generic by Once's standard.