I'm not a witcher fan beyond the show but its my rather limited understanding then Yennefer is more or less Geralts Wife/Ciri's mom so it would make sense to give her a fair amount of build up leading into her and Geralt raising Ciri. So the First season is pretty much how Yenn got to be the yenn Geralt/Ciri know and Geralt trying to avoid fate just wanting to be a monster hunter before Ciri is forced on him.