If she hasn't cum out her soul into Lethicite (which I don't think she has), she's not a demon. She also hasn't demonstrated any self-transformative abilities, which is a hallmark of demonhood. As for whether she can become a demon in future content, it's realistically possible; the Wayfort she lives near is going to be home to the more corrupt non-companion followers, and as a highly corrupted individual herself it wouldn't take much for the Champion and/or some of said followers to push her over the edge if they wanted to.