Personally I would think Faith was well aware of what the Killstream is and what Ralph does. She'd been talking to him for a while. Teenage girls don't really care about stuff like that, they can change a lot in a short time if they meet a guy they think they have a future with. I remember my sister at a similar age going radical vegan just to make her boyfriend love her, then dropping it as soon as they split.
No, I think Faith has been trying to push the affair into a more serious relationship. Teenagers often do that because of their hormones and shit. We know she has been showing Ralph baby videos and hinting strongly at her desire to be a mother. Ralph sees her as teen pussy, nothing more. She probably pushed a bit too far one day, Ralph exploded in a fit of rage, said some horrible shit, and she left upset.
If her sudden need to be with her family is related to Ralph - and it's likely it is - then to me it reads like a teenage girl who's just had a bad breakup and needs love and validation from her parents.