Board Thread:Skyrim/@comment-138.130.248.19-20140204143906/@comment-2601:204:8600:4627:5CF9:8422:3379:EE83-20190120195229

If serana isn't at any of the two castles while your doing the unseen visions quest, then she will be at Ancestor Glade entrance. That's where I found her when I lost her.