Consciously naive?

BUMP

Life can only be understood backwards. It must be lived foward

I think it means exactly what it sounds. To be "consciously naive," I think means that she acts innocent but understands more than she lets on. Either that or she thinks she really is naive but she actually isn't. I think that is a good description of Cassandra, actually. As the narrator, and a teenager, she's still trying to figure out who she really is. Meanwhile she wants others to like her, and she probably feels under the shadow of her sister as well. So maybe as a defense mechanism, she acts "consciously naive." That way, she can observe and make mistakes without getting into too much trouble.

Or...I just shoot you - "baby."
- Special Agent Dana Scully

I think that Simon was saying that Cassandra was acting rather childish for her age. And yet it was that part of her personality that he found so attractive about her.