Board Thread:False Info and Speculative Discussion/@comment-3427796-20140820053526/@comment-11533671-20140821013759

I sort of figured it was related to how they stopped the Nogitsune. You can only possess one form at a time or something like that.

Lydia had always been a Banshee, further evidenced by her grandmother knowing she would crack the code when she hadn't been bitten yet. The bite just triggered her latent powers.

Idk...this could all be just speculation until or unless explained in the show.