Yeah, Yennefer is supposed to be the dominant one in that relationship really. There's rumours that she might a younger version of Yennefer, but then wouldn't that require a younger Geralt too?
Fringilla Vigo being cast so early is a bit odd, didn't she only turn up in like the second last book? They might change her back story to give her more relevance given they've race swapped her. She is Anna Henrietta's cousin, who is related to Emhyr, who is of course the father of Ciri.
I'm hoping they set it as Geralt and Ciri are travelling to Kaer Morhen and he is stelling her the short stories. Kind of like that old Jim Henson The Story Teller TV show. Which like The Witcher was kind of twisted fairy tales.