The aforementioned drugging may have rendered Kate's mindset disoriented and distorted, leaving her semi-conscious mind to hallucinate scenarios that either didn't take place or were entirely disjointed from the way they happened. Could that illusions plant seeds for the conception of Annabelle, who merely existed in Kate's imagination?
@bitchysoftie on Twitter posits that this imaginary Annabelle may have been given the same face as Jeanette in Kate's head. That could actually prove Jeanette's innocence, clearing her of all allegations.