User blog comment:MrAnonymous/Do you think Peter is a ghost?/@comment-190.177.251.168-20120612142833

Nah, I think this is all happening in Lydia's head, much like how S1 had Jackson's creepy hallucinations. I think whatever factor made her immune to the bite didn't quite manage to prevent Peter from leaving some psychic reside inside her (remember werewolves can pass on memories through clawing, like Derek did with Jackson or Peter did with Scott, so it's not unfathomable to imagine it could happen through biting as well), so the hallucinations are Lydia's way of dealing with that.