Like Janice, Carol also experiences a significant amount of demonic activity, even having to fend off a Demonic Possession in the climax. There's only one problem: Annabelle is explicitly only interested in Janice, and had already achieved its goal by the time Carol was attacked in the workshop. Not only that, but there was clearly activity before Annabelle was released by Janice, and Esther explicitly says it was unable to move beyond its trap in the closet, and the demon that stalks Carol looks nothing like Annabelle's true form, which can only lead to one conclusion: There is a second demon in the Mullins household and it's after Carol. And no one notices because they're too preoccupied dealing with Annabelle.
