Hmm... perhaps try doing some radiant quests, nothing major, then check back after you've done a few. If she's not there by then, try reloading an older save before you told her to leave. Also, is serana still your follower?
Hey guys I can't find the castle or place I first met Valerica I have ran around the Soul Carin a couple times. Is there a quest or something I need to obtain before I can tell Valerica that I killed her husband