I was with Serana at Castle Volkihar about to go into the Soul Cairn but I was having trouble finding the void salts. Not really being ready to do that quest yet anyway, I thought maybe I could find void salts elsewhere in Skyrim. So I left poor Serana by herself for several in-game weeks.
One day, I was trekking to Cragslane Cavern, the bandit cave hideaway where they engage in fighting of wolves, and as I approach it I am surprised that there are no bandits or wolves at the exterior is there usually are when I had not cleared this location for a while.
I soon found out why: Serena was there and had cleared out the exterior for me, and she was waiting for me
in one of the wolf cages outside the cave! As soon as I approached, her first words to me were “Having trouble finding those void salts? It cracked me up!