For some reason whilst serana was following me she disappeared, so I tried to get a new follower and was told I already had one, so I completed a companions quest in order to get farkas to follow me instead, then i dismissed him. Afterwards i returned to fort dawnguard where she should respawn but shes no where to be found. It's quite annoying, by the way I have complete all the dawnguard quests, has anyone else had this problem and can anyone help?